I think the best way to approach this is to talk to him about you seeing other people this will hopefully give you some perspective on your relationship. I personally know it can work wonders. If you are part of some NA type group, suggest to him that he comes with you to one. Give him opportunities to get comfortable so that you guys can talk and have a serious conversation. Just tell him exactly how you feel and what you want going forward, and if he isn't willing to put in at least half that effort he just might not come around. Best of luck!