Broken up for over a year, but dealing with it emotionally now

Brief overview: we broke up in Jan 2010 and at the time it was more of a weight lifted off of my shoulders then it was upsetting, I have been in a new relationship since July 2010 and my new bf has been great ever since i met him...about 3-4 months ago i started having random thoughts about my ex and now its hard to get him off of my mind...neither of us ever cheated, but there was jealousy and trust issues that were never really resolved and i guess we just couldnt deal with anymore....we were together for almost 5 years and the last 2 years were prob just arguing...I feel like I am now dealing with our break up after all this time which is pretty difficult especially since i am with someone new...i feel like i have emotionally pulled away from my new bf somewhat bc of trying to deal with the breakup of my ex...a part of me does not want to get over my ex and wants to have hope for us in the future and a part of me tells me that i need to just get past it all but i dont even know how to begin to deal with this...

i am also not sure if i should deal with this on my own or let my new bf know what is on my mind...i know that he has noticed that i have backed off a little bit and at times when i am upset thinking about the past with my ex and my current bf asks me what is the matter i just say that nothing is that matter...i dont know what to say to him...should i just be honest? or do i just deal with it on my own?