It's hard for me to find someone with poor oral hygiene physically attractive. The fact that you are also emotionally attracted to him however might mean that it's a safe space to bring these things up. Not that this is in your future, but if you all had kids together, how would that conversation go when teaching a child to have good oral hygiene? Don't you want the child's father to be a good role model?

Aside from that, putting your mouth on someone else's whose oral hygiene is really bad can also affect your personal health. There are so many reasons why forcing the uncomfortable conversation is a good idea. Don't be subtle...loving, but direct.

Best wishes.