I cannot espouse the benefits of going to therapy enough. My closest companion cheated on her husband for reasons similar to yours, and they saved their marriage by going to counseling and having a mediator to help them talk through their issues. Turns out the issue was HIS body image dirty laundry coupled with some mild depression that made arousal and drive non-existent. They forgave each other and moved on. However, I've also seen couples decide to end their marriage after therapy because sometimes physical issues are manifestations of some deep seated emotional problems in the relationship that one or both partners are not willing to change or work on.  So yeah, try to get him to go to therapy or the doctor. Maybe when he sees how important this is to you, he will try and work on it on his own as well. Best of luck shitlady.