Even I want to read it now...so leaving this reply in case you were able to find it
This sounds like "Non zero sum" I'm not sure tho
omg tysm i finally found it appreciate u fr
its fucked up shit but theyre so hot n the art is good (not saying the treatment towards the mc is excusable) honestly, the art makes me stay but hopefully the mc wont stay
I think it's
Non Zero Sum (Yaoi) https://www.mangago.me/read-manga/non_zero_sum/
the mc and 3 other boys went to vacation (theyre bffs) and there's this 1 dude who the mc has a crush on and another dude who keeps baving sex with the mc because of some agreements (its rape btw) and they kept having threesomes but suddenly another dude that went to the vacation found out about them having threesomes and tried to stop them but in the end they had a foursome (this a part of the story that i can only remember)