I have recently started my first D&D game using 5th edition (I'm the DM). For our first few sessions everything worked fine. The players all had fun and their characters were all developing. During my last session, one of the character's had a falling out with another (characters not players) so the character left the other two.
During that session I ran the two groups simultaneously (more or less). While the solo character left to explore a nearby forest, the others almost got killed by the villain (one of them did but he was revived).
I would say that this is probably a form of My Guy Syndrome due to the character leaving the party because that is what his character would have done. However, it is getting annoying because, while the larger group is progressing through the story, the solo character isn't really doing anything.
I can easily get the group back into the same place. My problem:
How can I get the party back together when two of the characters dislike each other?
Best Answer
Don't make it your problem.
Make it their problem. (The players).
If you don't want to run a split party, since it increases DM work load, then before the next game session begins you need to tell the players that you are not interested in running two games instead of one.
Core reason: DM's are allowed to have fun too.
Then, as you suggested yourself, set it up so that they come across each other.
Then let them role play the outcome. It may be resolved that they will never work together: not your issue, theirs. If that is how it works out, do as @Dan B suggests and have the loner become an NPC, roll up another PC.
If they work out a compromise, good. They have solved the problem, you haven't had to.
Here's the tricky part: they accuse you of railroading. Your response: I am not interested in running parallel games. We go back to DM's get to have fun too.
Since there are only three of them, it is to their advantage to hang together in a team based adventure game like D&D 5e. You should probably point that out as well.
If, on the other hand, you don't mind running parallel adventures, then there isn't a problem. Just do that, and do your best to share DM time as 2/3 to 1/3 (The player who splits off gets 1/3 of your time not half. Thanks to @Greenstone Walker for that recommended split in DM effort). The reason I provided the answer is that it appears that you do not wish to run parallel adventures.