I am not so sure this is a good thing to start up with an existing friend. I see this as risking disaster. I did have a FWB relationship for about a year but that occurred right from the start of the friendship. It actually was a very rewarding relationship. I got an outdoor adventuring partner out of it too. There not being any emotional investment in the friendship before the relationship started (we actually put an agreement in place) there was no emotional crash when the whole thing ended.