It's quite possible to have platonic friendships like that. I have a few truly platonic friends who are married women and I don't really know the husband (I am an unmarried male). Granted I haven't met any of them online... it's only been through work or school. Even though I've moved from the area, if I'm ever back I will email some of them and meet up for lunch, etc. It's no big deal and there is nothing nefarious about it. I would not assume his intent is cheating until he actually does something along those lines.