It's pretty reasonable you're annoyed. One of your fellow players secretly plotted to kill your character for revenge (and it worked), the DM - the one guy you pretty much have to be able to trust - was in on it, and your fellow players offered you no emotional support at a point when you clearly needed it and instead made things worse for you.
People have been annoyed over character deaths, but you also have the issue of a betrayal of trust.
Different groups (and different DMs) handle stuff like this in very different ways - some handle it well, some badly. You had a conflict within the party, and a conflict between two people, and some character death and secret plots on your hands. These are often things groups don't talk about beforehand, but should. As the DM, I wouldn't have allowed this secret plot and would've talked to you two outside the game to get this enmity settled at first signs.
(And honestly, if this was real out-of-game racism you were experiencing, I wouldn't have tolerated that either.)
So now the guy who betrayed you is the DM and you want revenge.
Don't do it.
A good plan is to decline the invitation, not play, leave, and find something else to do or another D&D group to play with. This is not advice for how to ruin Bob's day. This is advice for how to avoid having your own next two months ruined, and possibly several weeks or months after that as well, and instead have some degree of peace for yourself.
You're pissed off. But, proverbially:
Holding onto anger is like drinking poison and waiting for the other person to die.
— (Not sure who first said this)
So you're going to have several gaming sessions and two months in which you're busy being pissed off at Bob, stressed out working out how to get revenge, and suffering over the lot of it - and expecting him to suffer for it. Eventually. At some point. Maybe.
That's not working out in your benefit.
Here's how the next two months are going to pan out according to this plan.
- Bob's the DM. The universe of the game you're considering bends to his whims.
- He doesn't like you to begin with, resents you for something you did to him, and apparently is subtly vengeful. He might give you a hard time for the next two months. This is going to feed right back into you being even unhappier in general, and unhappy to be in that game. This may even increase the degree of revenge you want, something you might not even get to begin with.
- You're going to be preoccupied being annoyed at him and not really actually just enjoying a good game of D&D. (Not that this game is going to be a good game of D&D for you necessarily anyway.)
- Eventually, you might actually find a way to get back at him. But, since he's the absolute controller of the game's universe, he can just say: "Oh. Well, my guy's goddess smiles upon him and heals him. Then she teleports your character into the plane of fire. Alright, whose turn next?"
- Or you don't get anything out of it and you're just annoyed.
- Or a month in, before anything even really happens, he or your fellow players ask you to leave because you're not being very fun to play with. You probably won't be. You're here for revenge, not to enjoy a good game.
- And you're playing with this guy as your DM the whole time, again. That's worth repeating. Why would you want that?
This entire plan is toxic to you and you alone. It's going to be really unpleasant for you, and more likely than not won't get anything out of it - and if you do, it probably won't be very satisfying.
Don't do it.
But I really want revenge!
This is an issue between you and another person, not an issue D&D will help with. Don't try to solve it through D&D, and don't try to solve it by playing with this guy as a DM for a few months.
Deal with it out of the game somehow. Maybe talk to him and get stuff off your chest. Consider walking away and leaving it behind you rather than let this weigh on you. Different things work for different people. I don't know what will work for you, personally. But spend these two months of your life doing something else. Find peace, somehow.
A surprising option is forgiving him - and not for his benefit, but for yours. Forgiveness is just as often so you can stop holding onto the negative emotions you have - the ones which are affecting you much more than anyone else - and let them go and find some inner peace. You might not be prepared to do that, but I advise you try it.
D&D is normally not like this.
(But sometimes it can be.)
There are going to be groups more supportive of first time players. There are going to be groups where you can genuinely be friends with most people, get along with all of them, and reliably trust the DM and your fellow players. This wasn't one of them, clearly. I suggest you find a group that suits you if you want to keep playing D&D.
One thing that normally goes unrecognised is that several D&D players at the same table, playing the same session at the same time, are usually not even playing the same game. They have different expectations of what a good game constitutes, different ideas of what's OK and what's not, different understandings of the rules, and different opinions over how issues like loot and character death should be handled. Usually, they assume that everyone else shares a similar view, without realising that everyone probably thinks very differently - to each other, as well.
An analogy is having several people sitting around a table to play a game of cards, but they are playing different games: one person is playing Poker, another Hearts, and another Go Fish. That wouldn't work very well, but somehow that's how D&D gets played without anyone realising it.
This disconnect is the reason why someone authored the Same Page Tool - which, as its name suggests, exists to get people on the same page. Its author also wrote about The Roots of the Big Problems and A Way Out (from which I drew the card game analogy). All three of these links discuss this issue and the situations that arise from it, and how to deal with them.
This group was not on the same page as you, and were not what you were after. Another group might be.
This sounds like player behavior
I'm usually the one to point out way to address an issue in game. Not this time. I don't think this is a play style thing. From your description it sounds like this guy is having a little too much fun getting a rise out of you.
The player's behavior is really a bit out of line. Constantly hitting on every NPC of course requires you to play their part. (And that's been more fun for him than for you.) He may be hitting on you, or just trying to provoke a response. Either way it's not OK. You've made it clear this is no fun for you, and he hasn't changed his behavior.
The Details
Hitting on the celibate priestess, well that's just a little "challenge." There's no problem with someone wanting an in-game girlfriend who's a powerful figure like a chief priestess or a powerful adversary. Abandoning his party and getting a PC killed, that's not cool, and the other party members won't be real keen on that.
But that's all in-game stuff. And what you describe goes a little beyond that.
Respect
It all comes down to respect. If a player is disrespecting you (or anyone at your table) then that is cause to eject him from your game.
Fantasy vs. Realism
Since answering, the question has been updated to specify that "realistic relationships of all kind are OK." But while you might be able to encourage a person to be more sensitive and patient in a their courting efforts, it probably isn't realistic to expect them to fantasize what you want them to.
If the player would like to role-play like a chick magnet from a Heavy Metal comic, it's not likely you'll convince him it would be more fun if in-game courtship were more like "real life."
Going forward
If you're not ready to disinvite him yet, let the table know that the game is going Rated PG. (I'm guessing most of your players will be happy with this.) Don't role-play the romance with the fellow. You could allow the dice decide whether he impresses a female, and describe her reaction matter-of-factly, all in the third person, as boring as possible.
If he doesn't simmer down, you need to ask yourself if you are comfortable with the behavior. If you aren't, then he's got to go.
Best Answer
Good Old Session Zero
It seems pretty clear that you need to talk about what's going on with your players, and be a fair and understanding arbitrator so that everyone can enjoy the session, you especially. Proposing this can be as easy as saying, "Hey guys, I want to organize a little chat between all of us so we can all the most out of each session."
A few key points for facilitating a productive, exploratory talk between all parties involved, and also how to go about this talk when expulsion is the last possible option:
Don't be Accusatory, and Bring Balance to Each Opinion
In-game, there is a discrepancy between what your coworker wants out of his role-playing experience versus your other players. Out of game, he's a close friend of yours and works with you. Therefore, it's in your best interest to approach this in a manner that is compassionate and interested in all perspectives of the situation. Don't let your other players bully him, nor he bully anyone else.
It can be easy to gang up on a problem player, and usually, it's best to simply eject them from your party. In your situation, since this is not the optimal solution, you need to be able to facilitate an honest, open discussion between all of your players regarding his behavior.
How to Talk About His Behavior:
1) Keep the discussion exploratory, and figure out exactly what the other players want.
Your player sounds like he's interested in roleplaying but seems to be getting bored, and thus is creating situations that have dramatic resolutions. When they don't resolve in his way, he gets mad, and may think you're simply punishing him for moving the session forward. I have no idea, which is why it is imperative for you to find out why he acts out. He may act the way he does for a variety of reasons: it's up to you to see if you can reconcile the differences between your players to pull this group together.
2) Once you figure out what your players want, brainstorm ways to make those game interests meet, preferably with the players.
Ultimately, your party wants to have fun on an epic adventure. Once each player's desires are out in the open, become the arbitrator and focus on how each players' desires overlap and how everyone can get what they want. Your player may be reacting to a lack of dramatic conflict in your campaign, and thus it is your responsibility to create more interesting conflict should you want a better group dynamic.
3) Emphasize how other players feel when someone is making the gameplay experience unpleasant for others.
In my experience, very few players actually get enjoyment from making others feel bad. Most people are either unaware of their behavior (shocking), or feel bad themselves and act up to be heard. Talking about their behavior without condemnation but in frank terms helps bring reality to these players. This negative social frown should be enough to wizen up your coworker to his own habits, coupled with the feedback on how each player is going to get more of what they want out of the game.
Final Take-Aways:
We're all here to roll dice and have fun.
We're all friends (ideally).
There's no need to double-down or get serious, we're playing dice games.
Try not to piss off your co-worker/close friend, but do give him a healthy dosage of reality regarding his behavior and how it makes others feel. The more empathy you can bring to your group, the better.
Ultimately, You Cannot Control How Other People Feel, and It's Your Table
Should none of this work and your party still has irreconcilable differences with said problem player, it may be time for him to go. You're not a therapist that can work on his interpersonal issues or desires, and having an open ended discussion with your party may help him realize that whatever he's looking for at your group, he will not find.