The thing about surviving something truly tragic is that it changes your expectations forever. You make do with very little. You're grateful for crumbs. You make the best of small mercies. You endure large trials. You understand that life owes you nothing. You expect nothing, and when something wonderful happens, you don't trust it.
What was it about relationships that made you feel so vulnerable? Oh, right. A relationship. In any relationship, you put yourself out there. You exposed all of your sensitive nerve endings and your heart and you just had to hope that you trusted the right person.