BF wants a threesome with a guy

I (F) and my boyfriend have fantasized about threesomes from time to time. Although we've never really engaged in one, we have thought of hypothetical scenarios in case it does transpire.

He used to have preference for an MFF kind of threesome. Meanwhile, I would like an MMF one (but I never thought much about it). However, it doesn't matter because I really don't think that our sexual relationship would eventually lead to a threesome.

Anyway, the other day, he sent me a porn link that leads to an MMF threesome. Prior to doing phone sex earlier this evening, I asked about it and what position he'd prefer; he told me to guess so I just said "middle" because the guy there in the middle is the one fucking the girl and is simultaneously being fucked in the ass. Turns out, I was correct.

Fast forward, after we were done with our phone sex, I went back to the porn link to actually watch it and I was a bit stunned with how the guy in the middle was being fucked by a dominant-looking guy. Apologies for the sudden code-shift, pero medyo nabahala kasi ako upon watching the video like damn... does my boyfriend really want to get fucked in the ass like that?

There were times in the past that he used a butt plug while jerking off because I wanted him to and he was curious as well. When he did so, it was hot; I could also tell that he enjoyed the sensation of it.

In this case, I guess I just don't know how to feel about it and if it somehow translates to his unexplored sexuality. He's a typical straight man without the toxic masculinity. He has also liked bi-feminine guys and trans women content creators in the past but I'm not sure if it means anything because I consider trans women as women as well.

Should this be of concern? Do I talk to him about it? Please let me know your thoughts!

EDIT: I just want to clarify what I meant by bi-feminine men! Idk how to best explain it basta if mukhang babae natitipuhan niya. Meron kasi yung mga nagtatransition na mukhang straight guy at first tapos nagiging girly girl and bet ng boyf ko yung girl version. Sorry medyo magulo! Haha, additional context lang.