I can't recall if its manga or manhwa. It's about a girl whos going to meet some friends at a diner/cafe to introduce her boyfriend, but she found out the he was cheating on her by seeing him infront of a love hotel with another woman. As shes crying she sees a guy from her class. He has medium long dark hair and is wearing glasses. He kinda looks nerdy. She tells him that he has to go with her to meet her friends and makes him her boyfriend for the day. She takes him to change his clothes and she finds out hes attractive and when they goto the diner/cafe she feels bad and tries to tell her friends thats he not her boyfriend but he stops her instead. They eventually start having feelings for one another. Sorry for the long post but i've been trying to find this for the past few days and its driving me crazy. Thanks

It sounds like Are: After Boyfriend.

Thats it! Thanks a ton.