I get it, but please, don't fall into that trap. Mainly because it's horrible - you absolutely do not want him to hit you least of all in front of your son. I can also never get out of my head one post on here made years and years - probably a decade ago - where the poster always maintained that she'd leave for good if he ever hit him and then the day he did he almost killed her. It was an awful post, so frightening to read.
But also because it is never as pivotal as you imagine. What typically happens is that one day you are arguing and it seems like normal and then he will get up close to you and do something like push you out of the way, perhaps roughly, perhaps into a doorway or something, and you'll be thinking oh my god, did he really just do that? Does it count? What does that mean? And you'll still be in the thick of the argument so you won't have any brain space to process it and it will seem like such a huge overwhelming thing, that the most typical immediate response is "I wish that hadn't happened". And the argument will end and you'll be in this complete WTF headspace. But you'll go to bed, and in the morning you'll wake up and for a moment you'll forget and then suddenly it will come flooding back, and so will that feeling - I wish I could un-know it.
Then what happens is a very funny thing - because the consequences of dealing with it are so very difficult and because quite often the partner will simply go about their life acting as though it had never happened it is very very easy and incredibly tempting to simply rewrite history and decide that it didn't happen at all, you simply remembered wrongly, or interpreted the action wrongly, or it was an accident, or justifiably provoked, or it simply didn't count.
In fact, he might have already physically hurt you, and you haven't "codified" it as hitting, because of this very thing.
Then the longer you stay in this much more comfortable limbo the harder it is to look back and say no, that was serious, I should have acted - because your brain says well, why, if it was so serious, didn't you leave at the time? You can't leave now - you have lived with it all this time - that's ridiculous. And anyway things are fine now. He's doing better. Probably they will improve some more.
Don't wait for him to hit you - you will simply wait for the next time, for the worse time, for this, for that - forever. If you know that the relationship is unhealthy start making plans and researching options. It doesn't mean that you have to do them but if you need to - you will be ready.