The reason you offer for why they have to stay together is weak. No couple HAS to stay together. Especially when they are unhappy and unfulfilled which she clearly is. I'm assuming not every character she has slept with will be an end game option. Since she literally prefers everyone over the bf, anyone would do. A new character could be introduced who is more competent then the bf but still with flaws and not as good as the others that are end game options. As you said there are still 20-30 updates so it's not too late and it's not like new characters haven't been introduced recently. I agree the game has been set up for the cheating to be on the bf but in my opinion it was done very poorly and fails to include the aspects of cheating that make it enjoyable.
Sure she wants to hear his side of the story but let's be honest she's already checked out and already blames him for how things have played out. It's pretty obvious what he did since he was there with the other faction and she has to know this already. Is the expectation that he'll lie to her about what happened and she'll believe him? We all know he's going to tell her the truth. Even if he does lie, will she fully trust him going forward? Will she then put an end to the other relationships and be faithful? What will really change after speaking to him? She'll either resent him further for what he did or lose trust in him because those options are the only ways the game can go forward.
Most of your argument is that the story has progressed too far now and the dev can't go back so anything I have to say is pointless and not that what I say isn't logical or realistic. I've argued from a much earlier point in the story how the cheating route is flimsy and kind of ignores why it's thrilling and what makes it exciting such as the possibility of being caught or the possibility of losing things that are important but not being able to stop. When there are no consequences it can barely be called cheating. Her current position is no different then being single or him being a roommate or even a family member since there's nothing sexual going on for a long time. You can only argue that at this point in the story it doesn't make sense to change things with which I'm not sure I agree with but that's just changing the original point of the discussion which was the bf only being kept around so she technically has someone to cheat on and is simply a Macguffin and nothing else. You say she feels she owes him for what he did to help her in the past but has no issue doing anything with anyone else but him. Is that really being grateful or thankful to someone for their past help? Is that really the better choice then to end things and continue to lie and betray until it eventually is discovered and blows up? The disorder affects her with everyone else but him but that's not evidence that she feels basically nothing for him? I mean she's now going to either be an escort or a pornstar. What is the plan then? Keep lying and betraying but since he helped her so much in the past, stay with him like it's a favor? Like I said, the reasons to stay together are weak as hell especially when she's clearly happier with literally everyone else and is more emotionally and sexually satisfied with literally everyone else. I'm pretty sure someone stated the dev had to put him in a coma because he was so disliked by everyone but he still needed someone she could cheat on so just kept him around. Even the dev can agree he's just a Macguffin and has only one purpose but besides that is unimportant and has no real affect on the overall story. The only possible end route for him is being a cuckold and enjoying her sleeping with others as it's now impossible for it be only them two as she'll never feel the same way about him regardless of what happens. Can you really see a route where she stops what else she is doing and goes back to being faithful to him and living happily ever after? Now being unable or unwilling to have sex with him and constantly lying? If that's not possible, why stay together? She may be staying out of guilt or obligation but not because she genuinely cares for him. It's unrealistic to think they could have a happy ending just the two of them. Literally everyone can see it's over so the cheating doesn't really matter. Cheating on someone in a coma who has no way of finding out removes all the thrill and excitement especially when there's nothing to lose. Sure he may be important to her but it's only as a friend (if that) and not lover and is only doing worse by him with what she's doing so he clearly isn't that important. That is why I say he is a Macguffin and it doesn't make sense for her to stay with him.
The mental gymnastics it takes to think otherwise is mind boggling. The cognitive dissonance is strong.
