How to be on good terms with an ex?

I was with this guy for a year. He was really in love with me but he got really clingy. The problem was all of my friends were his friends too so I stayed in the relationship. But it got to the stage were I was starting to really hate him and it didn't help that sexually he hadn't a clue. He ended up making me sick just to look at him. My mam got ill so I had to be her carer so I ended up staying in all the time. I know it sounds bad but i didn't even break up with him, I just ignored him till he got the message. I did this because a) i'm a coward and b) I don't like to lie to people and hes really nice so i didn't want to tell him he made me want to hurl. He's not over me because my cousin says he won't go out with anyone else and he keeps trying to add me on Facebook. Anyway my cousin's 21st B Day is soon and he is going and I have to go so I'm panicking on how this is going to go down. Anybody have any suggestions on how to handle this situation? Also I Know I treated him like crap and feel bad enough about it so please don't judge.