violently preventing me from getting away during sex
during that time the sex got really rough
I've repeatedly asked to role back this and go back to 'nice' sex but it never works out
I always wanted to make him happy and so I accepted more and more extreme behaviour.
I'm choosing to stay and to consent to things I don't actually want. You are not consenting though, that is plain to see in your posts. You are relenting to his extremes because without that, you get no contact at all. And he isn't happy.
The use or not of a "safe" word here is moot, isn't it? Because he is actually preventing you removing yourself, so he KNOWS you don't want it. You have repeatedly asked for it to stop ... it doesn't. Does YOUR happiness not matter?
So I sort of give in to more and more until I'm laying there and just wanting it to be over. Sort of give in...to stop the pestering, the forcefulness of him grabbing you. You want it over, because you don't actaully want it in the first place.
I think no matter what happens I will always know that he will want to play out abusive situations during sex. And he doesn't care what you want/need/think. If you don't want to be playing out abusive situations, then he should respect that! This isn't about fantasy, this is about control. You aren't enjoying this, and he couldn't care less.
Relenting isn't consenting.
If you're not using a safe word or telling him to stop, there's difficulty. No there isn't. I get the feeling from op's post that she has tried to stop it (asking repeatedly????) and the answer is obv no op his part. Safe word would be ignored by him, I bet!
He would see it as a challenge.
It's not abusive but we are incompatible. SO WRONG!! Incompatible would be you trying the stuff he likes, you saying no, and going on to have "vanilla" sex which ultimately, you are both "ok" with, but not overwhelmed by. Incompatibility IS NOT him violently preventing you from stopping sexual contact!!!
He thought I wanted it. Even after you have REPEATEDLY asked him to roll back to 'nice sex'? He KNOWS you don't want it. He just also knows that you are so conditioned to make him happy, that you won't use the safe word...and even if you did...he would say "I didn't hear you/didn't think you meant it/I was too close to stop/I thought you didn't mean it"
I'm sorry, but to me, if you are engaging in that kind of activity, and have pre-arranged rules and a safe word, the responsibility is on you to use that word when you don't feel comfortable. Even though op has asked repeatedly repeatedly that it stops and they go back to "nice" stuff??? No, you are wrong. The onus isn't on her, because it is obvious that he has her exactly where he wants her, conditioned to making sure his needs are met, against her wishes!!
Safe words are for mutually enjoyable scenarios, between 2 adults who WANT THE SAME THING. They aren't there so one partner can freely abuse the other with "consent" because the other partner doesn't feel able to use the safe word
He thought I wanted it. I just wanted to make him happy and it was horrifying me that that's what extreme he would go to. He KNOWS you don't want, it #Electricaid, you have, in your own word REPEATEDLY told him you don't! He doesn't care! It's that simple.
And you find his extremes to continue sexual contact that you don't want horrifying! Sorry but all those saying "use your safe word" this is what the outcome is...op doesn't use her safe word because his extremes to over ride her are "horrifying" so she is trying to prevent it happening!
After that particular incident I explained that I should've used my word earlier and we had a long conversation about how important it is that I say it whenever I need to. So he has you excusing his terrible behaviour, doesn't he? YOU are apologising to HIM for the stress and discomfort HE caused you! Also, now he has free reign to do what he wants, because you pretty much have said that it is on YOU to stop him with the sage word. In reality, the word is meaningless, you don't use it because you are scared of the consequences of doing so. And now, he isn't going to stop until he hears it. 
I know I sound like a complete idiot for not just saying it but I can't explain how or why I acted like that in that moment. You froze. Quite common in cases of rape/sexual assault, it's a survival mechanism. As op said on the other thread you were on, she gave in to prevent an escalation of abuse. You do exactly the same.
Relenting isn't consenting, and neither is the lack of a safe word.
You are still fairly young, op but I will say this, a good partner will know when you do not want to do something. It sounds like you happily talk about the issues you face, but he is actively choosing to ignore your wishes.
I feel like I did make it clear when I said I wanted to roll back all consent. That I wanted him to make sure I was happy with absolutely anything before going ahead. He doesn't. Says it all, doesn't it.