They are open to new experiences, including FWB hookups. They will not express their emotions if their heart is hurt.
They prioritize platonic relationships above sensual ones. They wouldn't put their significant other at danger by starting an FWB relationship with them.
They're not the kind to settle down, therefore FWB is perfect for them. It satisfies all of their needs without restricting their independence.
They struggle with generosity. Their egos are just too big. In their wildest nightmares, their FWB would hook up with someone else.
They don't have anything against casual sensual encounters, but they'd rather have a committed partner.
They're flattered whenever someone notices their talents. They're very into the concept of FWBs.
They are easily envious, thus being FWB with them might be problematic. Most of the time, they would feel terrible.
They are willing to try new things, thus an FWB relationship would be OK with them. If they could only find the proper guy.
They won't accept someone into their lives until they consider them to be significant, thus FWB won't work.
They probably wouldn't want to complicate matters. You two are either a unit or you aren't. They want either extreme or nothing at all.
They would probably fall in love with one other if they had an FWB relationship. Ultimately, it would lead to love (or heartache).