He has never laid a finger on you - until now. So sorry you're facing this shock, OP. Sometimes a person's reaction is to freeze and do nothing and this seems to have been your response. You're clearly ashamed of him because you hope nobody saw.
Firstly, yes, he has crossed a line. He hit you in anger. That was assault and probably ABH too. That doesn't mean you were injured, just that he made contact. He was 100% in the wrong here. You have some decisions to make about what you want to do and how you handle the changes his action introduces to the relationship.
You have seen a side to him you didn't know existed. Do resist the temptation to focus on him, his motivation, his feelings etc. Focus on yourself, your feelings, your plans and hopes. It doesn't matter why he did it, really, does it? Nothing could justify it or make it alright for him to hit you.
Sadly, most people who hit or assault a partner won't stop at one incident. It's sad too that incidents almost always escalate. If there are no consequences (except, presumably, you shutting up!) he will have no reason not to do it again, will he?
I think the two of you definitely need to discuss what happened with you taking the lead and expressing your refusal to be assaulted. Whatever your normal routine is and whatever he may expect, I suggest you stop all contact and let him contact you if he chooses to. Think hard what you want because you are clearly in deal-breaker territory here.
If he scoffs and minimises what he did, calling you ridiculous or oversensitive or lacking a sense of humour and passing it off as a joke or 'just a tap', your best course would be to end it right there. We call people who think and act like that entitled abusers. There is little chance of changing him and every chance it will get worse.
If he does that in public, what might he do behind closed doors?
And please don't listen to anger management suggestions. He was managing his anger alright, to control you!
Good luck,