Commitment issues??

Okay so, i've barely had serious relationships, and this is due to to fact that when i get too attached i get frustrated, i become antsy, overly emotional, a bit irrational, i get upset over nothing,i feel like i trust the person, but my expectations of them are quite low, like i expect them to be unfaithful etc, and it drives me crazy. i hate feeling so attached because of how ansty i get,but its ruining my relationships i've tried talking to my significant other, trying to give my all but i still end up feeling stressed how can i stop feeling this way?

In other words, you enter every relationship on the defensive and braced for something bad to happen/be done to you? Where does that come from do you think? Parents? Siblings? How old are you, if you don't mind my asking? And what quantity, specifically, is 'barely'?