I'd qualify that to be "non-dating website".

But actually, I wouldn't be surprised if somebody broke off an existing relationship to pursue someone they were fantasizing about online. If they're unhappy in their current relationship, online fantasy is a form of escape and leads to eventual idealization. By comparison, the real person can't compete as their flaws are evident.

Dime-store psychology perhaps, but on these topics nothing surprises me.

I think many of the attitudes regarding porn has changed simply because it became so ubiquitous that it changed culture, not that culture somehow grew up and grew to embrace porn.