The guy I used to live with didn't shower every day like I do. He's a musician and I guess that grungy thing makes him look cool.

Fortunately, he didn't get as smelly as some guys do -- didn't seem to sweat much. There were times I told him he reeked, though. Especially after a night playing in a bar, he would smell like whisky, skunky beer and dirty ashtrays. I would bring it up in sort of a joking way, something like... "Okay, you stink. Go hose off or you're not getting anywhere near me." So, he'd laugh, smell his pits, make a face, and then go take a shower.
I never made it a really serious issue. I figured if I approached him as if it was something very important and serious that we needed to have "a talk" about, that would have embarrassed him. He responded very well to me saying, "Yo, you stink!" though. We could both laugh about it. He would usually say something about how he hated showering because "it's just so tedious" but he would shower anyway.
Most of the guys I have known wouldn't be offended by being told they smelled bad -- because of the kind of guys they are. You know, the kind of guys who think farts are funny. So, it wasn't insulting to them like it would be to most women. I know I'm generalizing here, but it seems to me that a lot of guys wouldn't be as sensitive about that sort of thing. Maybe you're just imagining how awful YOU would feel if he said the same thing to you and projecting that? It seems that part of the reason you might be so worried about mentioning it to him is because you knows he gets defensive about your OCD issues sometimes, so I can understand why bringing up hygiene with him would make you nervous. I don't think this is an OCD issue, though. Most women don't want their man to smell bad. Period. I don't have OCD, but I don't want to smell a dirty man. I like things that smell nice and clean. Your bf might not be insulted at all. Can you bring it up in a light-hearted way so it doesn't seem like a big issue? He might be glad that you told him.
Another thought -- maybe changing the sheets -- giving yourself fresh sheets to sleep on would help you get a better rest? Make sure you always have a fresh spare set of sheets. I know people who don't have OCD who change the sheets everyday. (I'm lazy, so I only do it once a week.) It's so much nicer to sleep on freshly laundered sheets.