TLDR version:
Woman friend had grown too attached to her FWB.
Told him, it wasnt mutual.We (my wife) suggested "stop seeing him, at the very least, stop hooking up with him", she continues to hang out and hook up with him.

Then comes back home sad about it all.
any advice?

update: sorry things got REALLY busy at work, and I just got back.
THANKS FOR ALL THE COMMENTS!