I think, on a very primal level, without abuse, the human mind fears being left alone. Because, in truth, when we are children, we are incapable of caring for ourselves. In truth, if our parents or caregivers left us when we were infants, we would die. Despite our desire to think that we are above the animal kingdom, we are not. We all know what is going to happen to the bear cub who gets separated from his mother when we watch the Discovery channel.
That being said, when this natural fear of abandonment meets up with abuse, our brains go into a hypervigilant state of fear about being left. I know with my first serious relationship, I tried to control everything because of this fear. I was terrified of being alone. This resulted in being abuse toward my girlfriend. It is so messed up sometimes... the way the mind works. You are like this because someone abused you, and the fear that was created causes you to abuse in turn. It's fucked up.
Once I worked on my abandonment issue and stopped abusing/controlling her, we broke up. (Go figure.) My second long-term relationship was spent trying to convince myself (and my g/f) that I didn't need her, wasn't afraid of her leaving me, etc. Yeah, good one Sean.
So, I guess in a long-winded answer, I'm saying that this has definately plagued me. Still not sure where to go from here, except now that I am out of any relationship for the first time in 10 years, I am starting to realize that it is up to me now to take care of myself.
That I don't need anyone else to either take care of me or to answer to. It's not as scary as I thought it would be.