How do you stop thinking about an ex-boyfriend?

So many things remind me of him. Just when I think he's out of my mind he pops back in. I try and do different things that we never did. Nothing is working. Time is not healing all wounds. Please help.

Updates
It's been 3 months. We dated for 14 months. He's moved on with someone else already and I can't understand how he could do that.