I would get him medically checked out and include testing of his sex hormones/testosterone. Perhaps he has erection problems and avoids sex with you knowing his erections are not so good. And perhaps he is simply a man with a lower sex drive than you. of course this will be uncomfortable for both of you- him knowing he is not pleasing you sexually and you feeling sexually frustrated. Best get his medical side checked first then you should feel free to discuss your feelings with him- this is better than you walking away as you want to save his manhood. His manhood will be damaged if you leave him for his sexual non performance. Give him a chance to hear your heart.