Exes in themselves are not a threat.
Dear Dr. Romance,
Should a man expect a woman to want to become involved with him when he is still best friends with is ex-lover--and he is a renter in her house? He claims it is all over between them, but I don't see how he or the ex-lover should expect a woman to feel comfortable fitting into this arrangement. Please, I would love some perspective.
There's a lot of information I need to know before I can advise you. If he and his ex have been done with their relationship for a long time, yes, it might be OK. Exes in themselves are not a threat -- it's the nature of the friendship with the ex that could be a problem. Do they still have a romantic/sexual relationship?
The fact that he's still friends with his ex actually could be a good thing -- it probably means he didn't do anything awful in that relationship. The question is, do you trust him? Do you know him well enough?
Take your time, go slowly, and make friends with her. If you're close to her, you'll be able to see what's going on. If you actually care about him, then it's worth it to check things out. If you don't like what he's doing, don't expect him to leave his ex or end the friendship. It won't happen, and he'll hate you for it. If you make him choose, you'll be the one to go. "Handling The Green-Eyed Monster" will teach you everything you need to know about jealousy. "How to be Irresistible to Your Mate" and "No Cooperation? Solve it Yourself" will show you what to do to solve the problems. How to Be a Couple and Still Be Free will teach you the skills you need to know to make your relationship a success.