Wow, thank you so much for your reply!
I think you are right... But I brought this up to my fiance, that maybe I should tell him before he moved in and he (fiance) thought it was too soon and I was obsessing and shouldn't say anything (because fwb just got out of a relationship, etc.). But I think you have a real point...
And, if I can't bring this up to my fiance, then my chances of having any sort of romantic relationship with this guy (while I am with my fiance) are slim to none... Because if it's going to work, I need to feel like I can talk to him about anything still.
Sigh. I'm so scared! Lol. Having these feelings in the first place scared the shit out of me... Because I love my man with all my heart and we have this amazing relationship... If this thing with the other guy fucked it up, I'd be heartbroken. Yeah, I'd be sad if I had to end my relationship with the fwb... But no where near as upset as if I ended my relationship with my fiance.
Anyways, thank you so much for your response. You've really helped me. It's nice to just put the problem out there and get a thoughtful reply from someone who probably has at least some idea of what I'm going through, lol. None of my friends really would at all.