Well, first, I want to know if they have experience with a long term relationship, if parents divorced there's a strong chance they had issues with one of them.

Then you kinda have to do some sleuthing but you want to know if they have mommy or daddy issues. If it's daddy issues you can be pretty sure you're dealing with some kind of crazy. If it's mommy issues then they might be one of the Tom Boy types with lots of orbiters which is shitty because then every time they get mad at you they will run to one of the orbiters.

It takes some sleuthing but if you understand how someone grew up, you can get a pretty good idea of what emotional issues they'll have and then it's watching to see if they've worked on it or if they have no clue and are just psycho. lol