Well you guy were together for three years. That is a good amount of time to be in a relationship. This is why it is so hard for you to get out of you head, and it is completely normal. It could be because feel betrayed, like you did not have closure, or did not know why he did what he did. So yes I want to say that it really it normal. Especially when the relationship ended on hurtful circumstances.
The way way to get over these feelings in with time. That and you need to start being social and do things that you like. The more busy you are with things you enjoy, hopefully you will not have a chance to think about him as much as you do. Or even you have to make a cognitive decision not to think about him. Meaning that every time you do, then start to think about something else. Pretty soon, not thinking about him with come easier and you will be able to move on from him.
SLREED I have read up on this kind of thing and I have read that he was the one that didnt feel good enough and thats y he done it I still feel angry and when I think of the girl he is with I do feel jeoulous but people keep telling me that he will do the same to her but I want to get away from feeling like that and not care at all what happens to them both