What the hell is that logic, oh fell in love with your friend and then started getting intimate with him behind your back... hahaha so wholesome. Now if she would have left the MC first, or talked to the MC about it and come to an agreement to have a poly/open relationship or something, that can become wholesome. Going behind someone's back isn't wholesome unless it's a toxic marriage and your significant other is already cheating on you first, then It can be wholesome if you find someone who treats you better. That's the only example I can think of where going behind someone's back in a relationship is wholesome.