Why do I move on so fast?

All of my relationships are short (3-4 months) bit the last one I was in I thought I was in love. Got pregnant, lost the baby. Everything. We only broke up two weeks ago and I’ve already started talking to someone else and I’ve already lost feelings for my ex and have started to have a crush on this new guy. I’m 24 not a teenager or anything. But I’ve noticed that I always have done this. I always move on fast or lose feelings super fast after breaking up.