Confusing roller coaster of love - to wait or run?

So this is a bit of a long story!

I've known my friend Patrick for almost 3 years now. We haven't always been good friends, we've only kept in regular contact for the last 1-2 years. Over that time we've developed quite a strange connection. We regard each other as very good friends, even though we don't talk or see each other often.

I guess I started developing feelings for him 2 years ago. We exchanged phone numbers and were chatting and he had me all excited, as you feel when you meet someone you like for the first time. Then I found out he had a girlfriend so I put those feelings on ice and didn't think much of it. A couple of weeks later, when we were drunk, he almost cheated on his girlfriend with me and he asked me to be his girlfriend. I refused to sleep with him while he is in a relationship and told him we'd talk about it when we were sober - that never happened. A few weeks later they broke up and he went off the rails for a bit, drinking all the time, and I got turned off by his behaviour.

A few months later, when uni started back again, I started to develop feelings again. His wild behaviour calmed down and he became the Patrick I really liked. Yet again, however, he started dating another girl! But his relationship with this girl was very different. I could tell that he actually loved her, and it was wonderful to see. A few months later, they broke up and he went wild again, drinking every night and making himself very sick. Again, my feelings disappeared.

In April of this year I started developing feelings for him (again). One night we went out for his birthday with a group of friends. Long story short, he ended up coming back to my place and we spent the night together. I asked him out as well, and he said yes. The next morning, however, I changed my mind. I realised that his reputation for cheating on all his girlfriends and his wild behaviour were not ideal. And I still wasn't over my ex, who I only broke up with in March.

Since then, it has been a roller coaster. Later that week I realised I had made a mistake - I don't care what others think, I like him, we get along incredibly well and I'd love a relationship with him regardless of the opinions of others. However, it was too late. He told me that he was not in a good place and didn't want to hurt me. A week later he started dating his latest girlfriend.

His latest relationship has hurt me most. He doesn't love her, he has told me himself. When he was drunk one night, he told me that he doesn't care about her and should break up with her. He said to me that he's scared to date anyone who he actually loves or who loves him, after being hurt in the past. I decided the next day to confess my strong feelings for him, telling him that I'd still like a relationship sometime in the future. He told me that he was happy in his relationship and couldn't do that to his girlfriend. I appreciated his loyalty and left it like that, again put my feelings on ice.

Everything has been okay until a few days ago when he sent me a message early one morning telling me he had a dream about me. It was a sex dream, and he continued to explain the details. We then chatted a bit more and he was telling me how he struggles in relationships because he gets bored with the sex and craves something new. I counselled him a little, telling him that I'm sure there are ways to make it exciting still, etc.. We were talking about fantasies and he was saying that he never gets any opportunities to experience them. He then told me that he was turned on by our conversation and needed to go and pleasure himself, and he wanted to picture me whilst doing it.

Unfortunately, my feelings for him have again blossomed :-( I know it's not right. He's in a relationship, and nothing will probably happen with us in the future. Although there is lots I love about him, there are also huge negatives. But I just can't help but accept those and still want him so much. What should I do? When he first got with his girlfriend in April I told him I couldn't be friends with him anymore but he was distraught when I said that so I decided we could still be friends. I try to distance myself as much as I can from him, but we do group work together for uni so I have to talk to him regularly. I can't stop thinking about him again now...