It sounds to me as if you have been traumatised by something in your childhood. You say your parents live separately, so I suspect that they divorced when you were seven and a half, forcing you to choose between them before you were mature enough to make such a decision. This trauma has rendered you incapable of making decisions, hence you cannot decide which of your four girlfriends to let go.

It's time to realise that there was nothing you could do to prevent your father running off with your gym teacher, but there is something you can do about your current romantic situation. Ask yourself which girlfriend most closely resembles your mother - that is the one to chuck. You don't want to be dating somebody who could push their partner into the arms of a primary school teacher with her constant stamp-collecting obsession.