I seem to have a different perception to most on here.
That is an enormous leap to suggest that you think he's hurt you on purpose, regardless if there's been an atmosphere between you in the past. The fact you think he's capable of physical violence probably says enough about your relationship, regardless of what the truth is.
None of us were there. We have absolutely no way of knowing if he slipped or not. If he's never been violent before, it seems like quite a big escalation and as you say he was in a good mood, it's very out of the blue?
My best guess would be he slipped, your response was loud and exaggerated because you were shocked (and it hurt), and he's mortified. And maybe a bit angry at what seems like an overreaction. I have to say, you do seem to be making a bit of a drama over it - he fell on your shoulder/arm while you were seated and while I'm sure it hurt a bit when it happened, to be sat in the dark much later telling him "you don't care that you hurt my arm" seems wildly dramatic. So he's an arse for not being more genuinely apologetic at the time, and you're making a song and dance about a genuine accident and a small bump. You admit he said sorry straight away but your issue is that he didn't seem to be sorry enough for a simple trip and bump which you'd already yelled at him for.....yikes.
Of course, if you really think that he did it on purpose, then you need to LTB - no question. And tbh, as I said above, the fact that you're wondering whether it was deliberate or not is genuinely shocking and suggests you probably should be separating anyway. This is not a healthy relationship in any way. There are times when my DP can be a right shit-head but I can honestly say I would never ever consider him faking a slip to hurt me.