I must admit, I am stuck. I dont know where to go with the story I posted about Rajesh

I like the idea. His brother had another girl over, she left some things in his room. His girlfriend finds them, gets mad and accuses him of cheating and threatens to break it all off when they were planing a wedding for the future. His 12 year old brother claims the clothes are his to save his brothers relationship because he loves his family. He has a very self sacrificing loving nature. Now I am stuck and have no idea where to go

I have planed that she pushes him deeper and deeper into more humiliating situations. Takes him out shopping, makeup. But, why would she even believe for a second the clothes are his. So she knows all along and as she has him put on the clothes, he doesnt know how because hes 12. He wont know how to do a bra, do a dress, or any clue with makeup or hair. He learns it all hehe. He can call it all off and admit that it isnt his, but that would make her walk out on his brother.

So this is my problem, why would the girlfriend even do this at all if she doesn't believe it and it comes even more clear that he had no idea what he is doing. Why go though the effort of humiliating him instead of just walking out

Realism is what i'm going after.