Thanks for all your advice. So my question isn't really should I keep seeing him - no, I know I don't want that anymore. The question was more, how do I get him to leave me alone.

Yesterday I told him "I want out, leave me alone"
He said, okay, but I want to meet up first and have a drink together. So I said "no, we're not meeting up". And then I walked away. This may seem like empty words, but I never stood up to him before so he was sort of shocked. Of course, easier said than done. But so far he hasn't called/texted me, so that's a start.

To the question, why is he my best friend. That's because he's been really supportive since I got sick, at work but also if I needed someone to tell my story to (while crying, no sex). I do have other friends btw
Still confused, but I'm so done with this guy and really should be foccusing on my treatment. Will never understand why he doesn't feel guilty about all this, because thinking about it makes me feel sick. But perhaps you're right and he has different values.