When Chelsea's lease is up at her old apartment, she doesn't see a reason to renew it when she spends every night at her fiance's house.  Charlie, of course, disagrees.  After they have a nice little fight in front of everyone, Chelsea storms off and goes hom.  Alan convinces Charlie that he'll have to back to her place and ask her to move in to make things right and he does so... only to find out she already packed up her whole place.  She had faith in him.

Chelsea soon moves in and completely takes over Charlie's bedroom and bathroom and even brings her cat.  Charlie can't handle it and storms off to the bar.  Alan comes and meets him there and convinces Charlie to apologize.  Charlie comes back and as he apologizes, Alan realizes that Chelsea has taken over his room as a closet.  Not to mention, Charlie kicks him out of the garage spot and gives it to Chelsea. 

Alan thinks about moving out until he realize that it would, you know, cost money.  Charlie, meanwhile, rents out Chelsea's old apartment as a place to escape.