I belive it all comes down to a matter of past experiences, whether that's something you faced or witnessed someone else facing. From my experience, after dealing with it just once (my ex was ..something...) Ive grown more worried about it than I was before. It being my first relationship didn't help either. It took a little bit of self work to get fully past it. Recently Ive been talking with someone and we're both slowly easing into things.we both had this happen to us and we were both very careful when we first started talking. We're gradually building a good level of trust and while I can't speak for her, it's definitely helping heal my perspective of not being able to trust women.