I'll speak to this since I've recently been in this situation. I have no problems w/ a FWB situation...I've done it in the past and it worked well for me. This time around, though, I ended up developing feelings for the guy. Unfortunately, I didn't realize it until it was too late and he had a new girlfriend. After talking to some friends, though, I bit the bullet and went ahead and told him about my feelings for him. Turned out to be the best thing I could do (don't get me wrong, I still got rejected, LOL) and he told me that he was glad I told him b/c he values honesty above all else. Sure, it still didn't end up like I wanted it to...but at least I got it off my chest and got my answer instead of sitting around wondering for months what might have been.