This has very little to do with your boyfriend and everything to do with intimacy. Getting back with your ex is filled with the same issues that caused the break-up. You want to get back with him while you’re in the current relationship. While you were with your ex you cheated rather than try to talk about the intimacy issues between the two of you.
Your ex can always be the one that got away, which keeps you less connected to the man you’re with, and thinking about your ex is the way you keep yourself from getting closer to your current boyfriend.
If you want to talk about your ex, find a good therapist for individual therapy. You will ultimately drive your current boyfriend away if you keep talking to him about your ex.
In the meantime, write a letter to your ex that you do not send in which you write honestly about why you broke up with him. When you are done throw the letter away as it is the expression that is important — not the actual letter.
Start focusing on the good aspects of your current relationship with the man you are with now. Make your current relationship an intimacy and communication priority, but talk about feelings for your ex with your therapist.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral