Either I haven't looked deep enough, or there isn't many Bi-Poly male fantasy books, specifically Bi-Poly main character men. Barely any Male Polyamory fantasy stories at all! I try looking it up, and I mostly get Bi-Poly women books in plenty of different genres, or reality-based.
Honestly, bi men don't get rep that much. Gay men and straight men, yes. But not men attracted to more than 1.
I'm already planning a story with a bi male dating both a dude and a chick (not going to be on here, plan to write it when I have more freedom). But the issue is that there's hardly anything. Even for non-cis AMABs, or male-aligned AFABs (such as myself). It's mostly for cis women, queer or straight.
Hopefully in the next few years, that'll change. But for now, there's not that many (that I've seen so far).
Bi men, and non-hyper-sexual poly men, deserve rep. The only ones I can think up from the top of my head with bi/pan/etc men is Trials Of Apollo, Magnus Chase, and Silk & Steel. Though S&S is kind of a light erotica (The story is good, but I didn't know it was a light erotic when I found out about the book and got it). But not poly. And those are literally the only ones I can think of. And Runebinder may be leaning into poly, but I don't know yet (still need the other 2 books), though the MC is a gay dude, not attracted to women.
And no, Marvel Loki doesn't count. He's an actual being from a real religion, and it's also kinda reality-based. Like, with Runebinder, it does take place in our world, but it's a magic-run zombie apocalypse with this whole bit of lore behind the magic users, and people literally taking refuge in an old magic school. Marvel stuff is just...superheroes, villains, and anti-heroes and such in our world, but that's about it.
There may be more, but they're most likely reality-based coming-of-age drama stories. Anything outside of that, Bi and/or polyamory men (AMAB or otherwise) don't get much rep.
I've just been in the mood to read an IRL book (not digital) fantasy book with a Bi-Poly man. But there really isn't any. Hel, even digitally, even with fanfics, most of the time the polyship is a girl dating a dude and a chick. Even if (in fanfic aspects) the guy is canonically bisexual, which leaves room for exploration for writing.
Like, I look up Marshall Lee fanfics, and there's plenty of him with Gumball, plenty for female readers, plenty for male readers, and PLENTY of Marshall x FReader x Gumball. But only like very VERY little of FReader x Marshall x Gumball, even though (as with Marceline) he's canonically a bisexual man.
So both with original fantasy stories and fanfics, bisexual men, poly men, and bi-poly men hardly get rep (as far as I've looked), and that's honestly kind of depressing.
I'd very much like to a read a physical fantasy book with a bi-poly male. But there's really almost nothing.