The goodbye
Leda's preparing to take off. Mel comes to say she feels terrible. Leda calls her a bitch, among other things, and doesn't want to hear it.
M: Linds and I, we're a couple. And that means there's no room in our life or our bed for a third party, no matter how much we may care for her.
Leda says it was nice to be with Mel again, and seeing her and Linds so happy made her want to be a part of it.
L: Sometimes it gets a little lonely. You're lucky Mel, you know that.
M: Well maybe it's time you found someone of your own. L: I might just do that, babe. I might just do that.
They kiss goodbye, and then Leda's off.
She's had a similar realization as Ted this episode...that she wants a committed relationship, that substitutes and sexual adventures are no longer enough. It seems that every character comes to that realization on the show at one point or another, in their own way.