It's highly unlikely that Allison cheated on MC After Allison hate fuck scene, she says she had not been with other man since the break up + there is no NTR for this game
Allison's character will develop around forgiveness (forgive MC, start the relationship again) and depending on the behavior of the MC (cheating on her again or not) and her goals (single LI no cheating, friends with benefits, cuckqueen (doubt it since it's not a harem game, but the MC has cheated on her because she wasn't that sexual?)) during the game, they will stay together at the end, or not