Honestly it's very disturbing to me that he was going to do that to you without your consent. Even if it wasn't something sexual, it's still something that's painful for you, and it was on your butt. This doesn't seem like a "small trigger" at all. If my partner changed their mind and told me not to pop a pimple of theirs that they had previously asked me to pop, I would back off immediately - and I have a compulsive disorder that makes me obsess over picking at and popping pimples! It's so freaky and weird that he would say "you don't have a choice", especially if he knows what you've been through.

But even if he doesn't know - he should realize how terrifying this is to hear for women. It's literally your body! Honestly, I would even say that because he touched you (and hurt you) when you didn't want him to, you would be fully justified in calling this assault, no matter how small it might seem to you. You'd call it assault if a stranger came up to you and tried to pop a pimple on your face while you begged them to stop, right? This isn't any different because you know him better.

Even if he apologizes, I don't think you're obligated to move past this at all. He told you you didn't have a choice about being touched and made you flashback to being sexually abused. This is not normal or healthy of him.