Any human behavior can be taken to an unhealthy extreme. When a person is unable to stop a behavior that is causing him problems, then it is called a compulsion. I'm not optimistic about him being able to stop this without some form of outside help in the form of a therapist. Saying "I won't do it again" is a pie-crust promise -"Easily made and easily broken."
A lot of people see getting professional help as a drastic step. However, that's what it's going to take here. If he isn't willing to take that step, then you have a choice to make. Accept that he has this problem, or end the relationship. Before you proceed to marriage and/or children, ask yourself "Am I willing to deal with this for the rest of my life?"