Absentee dad for almost 5 years; wants him NOW!!!?

My ex disappeared right after my son's 4th birthday. My son will be 10 in October. I received a letter today from my ex that says he misses him, he "severly" cut back his drinking & he's getting married in Dec. He wants my son to come visit him (he lives 2000+ miles away) for a month this summer. He's paying child support (less than $50 a week) and only b/c it's court ordered. My son doesn't want to go. Do I have to let him? Our divorce papers state that he gets visitation 2 weeks of every summer - but that was while he was living here, before he disappeared!? Does it still apply? Does the fact that my son doesn't even know what his father LOOKS like count?