I've been a psychotherapist for more than thirty years, and I believe the answer to why people use sex to get their needs met is because they're not getting them met in other ways.
More importantly, you need to decide whether you want to stay with him or not, and what you want out of the relationship if you do. If you need help with what you want and deserve, or even deciding to stay or not, get some counseling from a certified psychotherapist. Look in your yellow pages, conduct an on-the-phone interview with the therapist to see if she's the person you want. I say she, because a woman will most likely be better able to understand what you're going through---but not necessarily. You have to decide which of the people you talk to sound like they understand you and could be helpful.
All best,