Not a good reason, but it's the reason the MC didn't.
He's an unfaithful jackass who only worsened her tsun. (I know she is lonely, has confidence issues, and trouble trusting people and I was willing to die fighting an army to save her, but look at that maids tits) If she had a decent MC love interest, she would have been adorable and dere 95 percent of the time.
Granted, she could have used some better friends too. The fact that so many people overlook Slut Princess's antics still surprises me to this day.