It's not. It's canon that she cheated on you, albeit by being blackmailed. You can seemingly just choose to move on or try to help her moving forward. If you take her path, though, in a phone call with her you hear him in the background, so she's still with him. But you only learn of all of this if you take her path and hear her out. Then the 'save the girl' plot starts. If you continuously reject her, though, the MC remains with the (correct) assumption that she just cheated on him without knowing about the blackmail.
Were it irl. . . that kind of thing would deserve some form of help while the chick keeping her silence on the truth would really challenge any form of relationship continual.
Yes, grateful the SO would go far out for ones loved ones. But most anyone will agree that infidelity was too far and would have preferred she come to him and work together instead of surrendering.
[edit: based on what some comments later say. She did beg him to talk. I don't know if it was about the relationship or about the blackmailing.]
[I unfortunately have to agree with the comments that say, the mc really looks like he still very immature]
However.
TLDR: this a game. And with this being a stinking mix or romance-ntr, don't need that when ntr really does the opposite of giving me a good time relaxing. IRL, a respectful friendship might be required while a relationship continuing would be different strokes for different folks.