Season synopsis
Contains spoilers for this season and earlier seasons.
Charlie begins the season trying to keep Alan from returning to Judith, while a new relationship with Mia gradually challenges his usual rules. Mia expects a more serious partnership, and Charlie tries to adjust to her wish for commitment, including the possibility of marriage. Alan, meanwhile, starts dating Kandi, one of Charlie's former girlfriends. Their age difference and her limited interest in the practical details of adult life make Alan's relationship a source of friction in Charlie's house. Alan's budget suffers as he pays Kandi's bills, and the strain becomes more visible after she moves in. His efforts to help her find work and his attempts to keep up with the relationship leave him increasingly dependent on Charlie's house and patience.
Kandi moves in with Alan, and the brothers' romantic choices begin to reshape the household. Alan's attention drifts toward Jake's teacher, while Charlie and Mia try to reconcile their different expectations. When Mia returns near the end of the season, Charlie proposes and the two make wedding plans. Their families' meeting turns hostile, and the couple shifts toward a small Las Vegas ceremony. Charlie calls off the wedding when Mia says Alan must move out to make room for a nursery. Alan then proposes to Kandi, who accepts; he tells Charlie he will leave anyway, and Charlie is left alone with the consequences of both relationships changing at once.