How can I make my boyfriend shower more often?

Okay, I have looked at all the similar posts to this and I have tried everything. My boyfriend and I have been together for the past 2 1/2 years and I love him to death. He is extremely hardworking, loyal, and is everything I could ever wish for. We are high school sweethearts. He is the only person I have ever been with romantically and I never want that to change. I plan on being with him for the rest of my life. I just have a huge issue with his poor hygiene. The kid could seriously go weeks without showering. We fight about it all the time. I just have a really sensitive nose and his smelly breath and stinky a** seriously bring me to a breaking point. There have been a few times that I have even threatened to leave him because of it. I hate feeling like such a nag too...I feel like I shouldn't have to be his mom but if I never said anything he would never do it. He says it's because he hates water. He weighs like 112 and is 5'9 so he is very skinny and whenever he gets out of the shower he is freezing. I bought him a big fuzzy robe to wear afterwards but I guess it doesn't help. Ive tried being nice, sex in the shower, denying sex (although it doesn't seem to bother him which kinda breaks my heart so I wind up begging him for it eventually) I've bought him really yummy smelling cologne and body wash but he doesn't seem to like the smell. Also he has really bad skin issues, like he has really bad dandruff and to be honest, it really grosses me out. I've been a complete ***** about it and all he does is go in the other room and ignore me. I feel like he doesn't care about how I feel sometimes. It's not like he has b.o or anything, his butt just reallllly smells and his hair gets pretty lanky and greasy. I just hate it so much, but I love him sooooo much! I've tried dropping hints about how much I like it when he does shower, I've seriously tried EVERYTHING. I'm at my wits end. I really wish he would shave too...he just has a low self esteem and simply doesn't care about his appearance. I know he is always really professional with his job as well and I try to tell him it's important to look professional too but he just doesn't seem to care. Its not like I'm a clean freak either, I'm pretty lax on myself as in it's okay to skip a shower every once and awhile if I'm tired or something from work. I'm just mostly afraid that if we eventually have children, I just don't want my kids to pick on his bad habits. I just don't know what to do, please help!