The episode you are looking for is called
Here is the quote:
JERRY: So, you think Clyde told him?
ELAINE: He wrote a song about it!
JERRY: Well, maybe it's a good thing.
ELAINE: No! It's not a good thing! It's a bad thing! Do you know what this is like? To have no control over a relationship? And - and you feel sick to your stomach all the time? Do you know what that's like?
JERRY: No, but I've read articles and I must say it, doesn't sound very pleasant.
ELAINE: You know, one of these days, something terrible is gonna happen to you. It has to!
JERRY: No. I'm gonna be just fine, but as far as your situation, you're seeing him tonight so talk to him about it.
Good luck with the sermon.