I've noticed a lot of the people who say "Oh, you haven't met the right man yet" are people who believe in the One True Love, the Soulmate, the Accident of Fate to Whom No One Else can Compare. I've wanted to ask those people "Oh, what happens if the right man died in infancy?" but I haven't yet.
This is, however, the first time I've heard of someone saying it to a person who is currently in a happy, committed relationship.