Very confused, should I stay with him??

Sorry this will be a long post, my boyfriend and I have been together over 2 years now. We live together and there's talk of engagement. Anyway, after the first few months it became obvious he had a brain lesion(AVM) and this was obviously very stressful for us both. I was very supportive and attended every consultation, dropped everything when he needed me, understood when he told me he suffered horrendous migraines when we had sex and therefore we stopped. He's behaviour staged over time so started doing some digging. Well I wish I hadn't, I found dating websites (apparently he was looking for me on them), starting watching porn (he never has done) and I found emails of him contacting prostitues which I just couldn't believe seeing as though were are skint but trying to save money for a house. Everytime I have brought up my concerns just to be screamed at. I stuck with him thinking that maybe he felt unsupported through his treatment etc but months on....still no sex. Still sketchy behaviour and still shouts and through a a paddy when I sit down and talk to him. What the hell do I do??? I'm so confused, my limited confidence is non existent, I'm back in antidepressants and I don't know if I trust him anymore. My step dad has been diagnosed terminally ill and I feel that I need support not to be shouted at. Humph. A very defeated 24 year old.