Taxi (1978)

Season 4, episode 2

Alex and Elaine decide to take a vacation together through Europe. However, Alex feels it necessary to tell Elaine in no uncertain terms that they are going together as platonic friends, so there's no resentment if he meets and wants to spend time with any other ladies on vacation. Elaine agrees to this and they decide to do things mostly separately during the days, but to meet up once a day to write post cards together. During the trip, it turns out that Elaine is getting all the action, while Alex is lonely and unhappy. The last night, however, Elaine takes pity on Alex (more or less) and propositions him, suggesting that their friendship is strong enough to endure one night of ""love."" They then go off together...