Charlie must make a difficult decision about his future and with which woman he wants to spend his life: Chelsea or Mia.
When Chelsea convinces Charlie to let Alan's new girlfriend, Melissa, move in, the girls end up taking over Charlie's house.
Alan ends up playing maid to Judith's new baby as well as his former mother-in-law. Meanwhile, Jake uses an incriminating photo to blackmail Charlie.
Alan starts working for Evelyn as Charlie works to fix the relationship between Chelsea and Jake.
Jake stops at nothing to get away from Charlie and Alan, after they embarrass him out in public.
Alan's advice to Chelsea that she get breast-reduction surgery is not met with enthusiasm by Charlie, who kicks him out, but staying with Evelyn has its own challenges.
Alan and Charlie are shocked when they wake up next to a strange woman, and try to find out what happened.
While overcoming a bad break-up, Chelsea invites her beautiful college roommate to stay at the house.
Charlie discovers he has not been satisfying Chelsea; Alan attempts to cure his thinning hair without spending much money.
Charlie discovers that Chelsea has not been completely honest about her finances.
Jake is taught the art of infidelity by Charlie, whose girlfriend is away for Christmas.
Jake hopes to win back Celeste by writing her love songs. Alan and Herb hope to keep Judith from finding out they've become friends.
Charlie opts to have a colonoscopy in order to avoid going on a trip with Chelsea to see her parents. However, when he returns home, he finds her parents at his house.
Charlie suspects Chelsea likes the lawyer representing Alan after his arrest for a bar fight.
Chelsea and Charlie's relationship is at risk when Charlie's jealousy comes between them.
Charlie runs off to Vegas and returns with a new wife, but she's not Chelsea.
Charlie and Chelsea have a post-breakup one-night stand.
Charlie has a return engagement with Chelsea's best friend, while Alan has an unexpected effect on a new female patient.
Alan is torn between the bad influence of Jake's new friend and the hotness of his mother.
Alan tries for an intimate night at a hotel with his new girlfriend, while Charlie takes a different approach to obtain the "girlfriend experience"
Charlie is visited by the ghosts of his ex-girlfriends while Alan and Jake are on a road trip.
Charlie is miffed over Alan's planned attendance of Chelsea's birthday party and suffers the indignity of having Jake chauffer him around following a license suspension.