I wasn't commenting on your post specifically, by the way,i was just commenting generally.
, to me FWB doesn't exclude fluid bonding simply because I don't view it as a romantic gesture. I have/have had FWB that I would fluid bond with simply because I know they have similar ideas to me about it and are vigilant with their sexual health. That's what it's about for me, being vigilant with your sexual health and being able to trust someone is vigilant. As far as metamours go, I strongly believe that if I trust my partner,i can trust that they wouldn't consider fluid bonding with someone who wasn't vigilant with their sexual health. Someone I slept with recently seemed perfectly happy to try and have unprotected sex without asking me anything to do with recent tests, fluid bonded partners or anything to do with the subject. Normally, I speak about these things but it didn't seem relevant so early on... Of course we are going to use condoms... Everyone would.. Apparently not. That ruled him out for ever being considered for fluid bonding.
All in all, I dint think the trust level required to fluid bond is exclusive to romantic relationships.