DSS (18), lives with us f/t. He's been going out with this girl for 2 years which is an impressive length of time for a teenage relationship. His GF is a nice girl but comes from a troubled background which has obviously left its mark (and continues to). Her homelife is very chaotic and she finds a lot of stability from DSS and to a lesser extent from us and our home. She's here all the time.
They broke up over easter and she was outside crying, calling at all hours and threatening to hurt herself. I can remember being a depressed teenage girl and have a lot of compassion for her but this really isn't what I want for DSS. He's already chosen to apply to uni near home so he can be with her rather than going where the best courses are. Any time he's mentioned something he aspires to which doesn't include her (for example he said he'd like to teach english abroad, she started yelling at him for thinking she's not good enough), there's huge drama.
To be honest I am concerned she's going to end up pregnant or similar. We have spoken to DSS very frankly about contraception and everything and he's being careful but he has also said he feels trapped by her and her reactions to his life. She tried to talk him into dropping out of college 
DH is getting increasingly concerned too as he had assumed it would run its course when DSS finished his exams and went away for uni. I really feel for this girl but I'm worried DSS is getting into something he shouldn't be.