[bWg]

It sounds to me like he is finishing and not telling you. It sounds like he's embarrassed and uses an excuse to stop.

As for the largest size being "too tight for him to wear," that isn't very likely. Condoms are supposed to be tight and they have sizes to accommodate nearly any size penis. He may not find them as comfortable or pleasurable as without. This is not a reason to have unprotected sex.

Even if you are on some form of birth control I would highly recommend using condoms as well.

I would strongly recommend talking to him about both the "issue" and especially about the non-use of condoms. No matter the cost. If you have to refuse to have sex with him until he agrees to talk to you, then so be it.