or is it just about the sex?
How old is he now? If over 18 (hence not illegal, sex with a minor thing) then everyone should just butt out. I think he is just infatuated with an older woman (many young boys are with their teachers in particular around 15, 16 years of age, some later) and she enjoys attention and the fact that she can still sweep a young bloke off his feet at 49. It will pass, cut them a little slack. In fact, more everyone turn against him more likely is he to run into something even more stupid like a marriage.