Learn English – Screw with somebody

Let's start with removing idioms and colloquialism

In a relationship, you need somebody who will complain when you've done something wrong, and not someone who ignores (forgives) your faults.

First, "gonna" is a colloquialism for "going to". The standard future form "somebody who is going to..."

"Call you out" is an idiom meaning in this context telling - sometimes even in a harsh way - that you did something wrong; reacting to your doing.

"let something slide" is an idiom that means overlooking/ignoring some fault on purpose. Say, you were going 80mph on a road with speed limit of 60mph. There was a policeman with a radar, and they did notice you speeding. They did not stop you, no ticket, no fine, nothing - they let it slide. It's not the same as not seeing the fault - it's choosing not to do anything about it.

Your original sentence means that for a successful relationship you need a honest feedback from your partner. If something you do ires them, they should tell you. If you keep doing something wrong and they never protest, it damages the relationship.

Yes. Although "rounded off" usually applies to outside corners -- for example, the corners on a bolt head that allow a wrench to grip -- it can apply to inside corners as well. Given this use of the term, it seems likely that these are Phillips head screws. A crosspoint driver needs those inside corners to grip.

Paint was removed from (at least some of) the screw head slots. The screw heads were undamaged. Even so, the screws wouldn't turn.