Stuck in the middle.... Guy problems

I'm not sure what it is. I'm in a new relationship and life and so is my ex. No matter what I do I can't stop thinking about my ex and my past with him. These feelings don't go away. My ex was a dirtbag to say the least. But I've never loved someone so much in my life... When things were good with him i don't think I've ever been happier. With my current boyfriend he's great but he's either at work or playing video games. I feel he doesn't make that much of an effort in our relationship which is probably the reason why I'm missing an old guy. I'm even wondering if I resent him because he isn't my ex. Idk im going crazy. What is everyone's thoughts?