Romantically Constipated

Being entirely unable to engage romantically in a healthy fashion, either through the person's own fault, their own simple dislike of romantic relations, or the stupidity of their romantic choices. Most often, it is used to describe someone who leaves a relationship once things become more emotional. It can also describe someone who repeatedly engages in harmful romantic relationships, however.

You only left her because you started to feel something for her. That's what always happens with you - you're romantically constipated.