I could do with a bit of advice

I've been with my partner for about two years now, we've lived together on and off for a while (We both go to different Universities so we were constantly moving back and forth) but this year we decided to move in together with a couple of our friends for our final year.This is all going well apart from a few problems, a couple of months before I had met my boyfriend I was raped by a guy when I decided I didn't want to sleep with him anymore. This caused a whole bunch of health issues and probably some psychological damage too. I had only just lost my virginity a few months before that and was just starting to get used to bottoming (I don't enjoy topping at all) and the trauma of the incident left me having trouble going to the bathroom let alone having anal sex with anyone.Basically my boyfriend has a much higher sex drive than me and has, to put it bluntly, a pretty big dick. But since moving in together it's been starting to get a bit too much for me to handle the constant pestering for sex and due to what happened before I met him I can't have anal sex with him without pain or severe discomfort; so we can only do oral sex at most.We have also decided to try an open relationship (He is newly bi and wants to try other guys and I'm trying to see if I can take someone who is a lot smaller than him). I have met up with a guy a couple of times, he's a lot smaller than my boyfriend so I can take him with only mild discomfort, but I find myself enjoying sex with him a lot more than with my boyfriend due to the fact we can have anal sex without it being painful.This has sparked a lot of jealousy from my partner and caused countless arguments but I can't seem to get him to understand that I feel this is the only way I can get over what happened to me the other year (I've tried toys, they don't have the same reaction or sensation as sex does). It really upsets me when we argue over the fact I don't want to have sex with him (usually because I'm just not in the mood) because its a very similar scenario as when I was raped. I have told him multiple times why this upsets me but he claims his depression causes him to forget everyone else and focus solely on his own needs and then apologises constantly to me until I say I forgive him, which I feel is a problem all in its own as it leaves me without a cooldown period and having to pretend everything is ok.-Does anyone have any advice on what I could do? I feel if these arguments continue like this I'll have to call the relationship off as it is starting to affect my university work.