I have been searching high and low for such poly. It’s hard to find. Here’s the best I got. If someone else has something to add, PLEASE DO!
Of course this is only a Oneshot dj, but it’s beautiful!
https://www.mangago.me/read-manga/3p_shingeki_no_kyojin_dj/
This one is nice because they all like each other differently, and it takes time to get there.
https://www.mangago.me/read-manga/choco_strawberry_vanilla/
This one is good. It’s also omegaverse.
https://www.mangago.me/read-manga/ai_to_makoto_moriyo/
And those are the best I got. Most of the other ones I have are the two of them like the third and somewhat tolerate the other, or feel neutral towards the other at best. Not that they’re bad, necessarily.
There’s also two I know where the relationship/romance is not the focus, but the guy gets married to two girls, and they have all have a solid conversation about it, if you’re interested.
Though, to be honest, any romance with serious conversation as opposed to fights, drama, and miscommunication immediately has my attention. XD

Not the one that has 2 tops 1 bottom, or the opposite of that.They should all like the each other like 1 both like 2 and 3, 2 like 1 and 3 LIKE THAT THEY ALL YEARN FOR EACH OTHER DO U GET MESHSJSJSJSN