I'm not sure where or not I'd call myself ace, but I very much do not want to have sex at this point in my life (and the thought of it makes me pretty uncomfortable).

It definitely wasn't ok for your partner to tell his friends about the two of you having sex unless you consent to him telling them. That is a major violation of your privacy.

I don't know what to say about your situation that could solve the problem: you absolutely have the right to say no to sex with him or to not initiate (although I know that not initiating when there is pressure to can be hard; I've been in similar situations myself). I think it's clear, though, that having sex with him is upsetting you and that needs to be addressed. As hard as it is to bring it up, I would say it's better to tell him directly what is going on - he does know that you're ace, right? If you simply avoid initiating or say "not now," he will probably continue to pursue it later and follow the status quo.

I'm sorry I can't do more to help you; I know what it's like to be in a situation where you don't want to have sex with a partner who expects it even if he isn't forceful about it. I handled it by mostly pushing things off until we broke up, but I don't know whether that was a good idea or not.