Sims 3 moving in help?

okay so i am trying to make my male sim move in with his girlfriend or more have her move into his house it is an extremely nice place so i don't want to leave it so please help because he asked her she said yes but then when the move popped up there were no options i couldn't move her in to his place or him into hers and i have tried it twice i really want them to get married to please help