Quote from Ross in The One with the Flashback
Phoebe: What is wrong? Ross: My marriage. I think my marriage is kind of over. Phoebe: Oh, no. Why? Ross: Because Carol's a lesbian. And I'm not one. And apparently it's not a mix-and-match situation. Phoebe: Oh, my God. I don't believe it. Oh, you poor bunny. Ross: I'm an idiot. I mean, I should have seen it. I mean, Carol and I would be out, and she'd see some beautiful woman and she'd be, "Ross, look at her." And I'd think, "God, my wife is cool." Phoebe: Hey, do you think that Susan person is her lover? Ross: Well, now I do!