Not always
My gf is bi and will actively send me pictures of models of characters calling them hot and asking if I think they are
It's pretty nice to have a gf that you can actively call people hot too
You could swing it into a reflex angle by considering that such a question is quite normal in polyamory (not throuples triads specifically). I tend to date women who are bi or pan, and we'll regularly bring up people we find attractive. Hell, I had a partner go up to a bartender to give her number to her once while we were out on a date. It made me smile to see her shoot her shot like that!
I'm bi and every relationship I've had was like this. Drooling over people and characters together is just something I like to do in relationships. It's a fun bonding activity. Plus it's weirdly good for my self confidence for somebody to be drooling over somebody else who even I know is hot as fuck but they still clearly want to be with me more.