[Garasu Hokou] Moshi Futari kara Douji ni Kokuhaku Saretara ~Tsuki-kun Hen~ | Suppose Two People Confessed To You At The Same Time! ~Runa's Bit~ [English] [Mr_Person]
To be fair as long as all 3 parties are fine with it and gave consent i don't see why it wouldn't work, also, i saw a lot of doujinshis where the guy just stays with more than one person tho