People grow, people adapt, people change. Yes, they both made mistakes in the past and MC burried the relationship when he cheated but that doesn't mean that it cannot be fixed whether in game or in real life. Although in real life it is way more difficult, almost impossible to trust your partner again after they cheated on you.
At the end of the day these games are player fantasy so of course MC and Allison will have happy ending together on the reconcilliation path. I like that the devs went and tackled someting not many avns do, just wish I liked how they write MC on her path.