I've been dealing with this with one of my ex's for over a year now, just ignore him, not in a mean way, let him down gently, but eventually you will just have to be honest with him, tell him straight out. Then just move on, he will get the picture and eventually leave you alone.
Just keep moving on...I still love my first love but we stopped communicating for 6 years before we became friends again. Had to have time to heal and move on. Now we're fine with the fact that we're with other people