In the season eight finale, Sheldon and Amy get into a fight about commitment on their fifth anniversary. Amy tells Sheldon that she needs to think about the future of their relationship, unaware that Sheldon was about to propose to her. Season nine sees Sheldon harassing Amy about making up her mind until she breaks up with him. Both struggle with singlehood and trying to be friends for the next few weeks until they reunite in episode ten and have sex for the first time on Amy's birthday. In season ten, Amy's apartment is flooded, and she and Sheldon decide to move in together into Penny's apartment as part of a five-week experiment to determine compatibility with each other's living habits. It goes well and they decide to make the arrangement permanent.