Yea i can get that is critical to her character development especially now that i have finished the the Chloe+Rose Solo, though i think he could have acheived a similar result by moving that conversation to before the actual scene but thats just personal opinion. Also dont think he needed to hear what was going on to know it happened, especially with the scenes after that clearly showing she slept with him.To be fair, even though I primarily agree with what you said here, it seems like this scene is actually critical for Rose as a character and her development going forward from that point as well as her relationship with the MC, since you're apparently given the option of letting her know that that experience hurt you. In that context, I'd say it would be necessary for the MC to overhear it, as fucked as it is, so that he is at least knowledgeable of it having occurred and having a legitimate reason to be hurt by it, since he's from all the context I can gather without having played it myself, possibly starting to have feelings for Rose at this point in time. It's also necessary for Rose herself to have done it, so that she can learn the difference between sex with someone that is only using her for her pussy and sex with someone that legitimately cares for her, if not flat out loves her.
But ultimately i did like the game and only have a few minor complaints besides that. Some of the animations were kinda meh and some of the scenes were pretty dark and hard to see (i was playing with the Visual Mod which is supposed to help though i am not sure how much it actually did). And i did not fully understand why should have to hide that they are in a polyamorous relationship. As Rose said this is 2018 (in game at least) and there is nothing illegal about that in most western countries to my knowledge. But that's just nitpicking i guess.