Some may recall the episode where Mr. Burns was forced to hire a female employee at the nuclear plant, Mindy Simmons.
Homer immediately develops a crush on his sexy new co-worker, which freaks him out. His pal Barney suggests Homer get to know Mindy, proving that their attraction is simply physical. However, this only makes things worse as Homer quickly discovers that they share many similarities, such as a fondness for beer, junk food and TV.
Homer tries to avoid seeing Mindy at work, but they keep awkwardly bumping into each other. Homer tries calling a crisis hotline, but ends up confessing to Ned Flanders, who then proceeds to call Marge and tell her.
Homer panics, falls over and, and is knocked unconscious. During this time, he is visited by his guardian angel, taking the form of Colonel Klink, who shows him how terrible his life would be if he left Marge and married Mindy. This plan backfires as it reveals that Homer and Mindy would be incredibly wealthy and very happily married, and Marge would be the President of the United States.
Eventually, Homer decides to tell Mindy that they should avoid each other from there on. Mr. Burns, seeing the conversation from a distance, mistakes their awkward conversation for one between close friends, and selects them to represent the nuclear power plant at the National Energy Convention in Capital City, staying at the Capital City Plaza Hotel.
There time at the hotel is awkward. When sharing a foot-long chilli dog, they "accidentally" kissed like Lady and the Tramp. After a romantic dinner (the prize for winning the Convention), they return to Homer's hotel room, and sit on the bed. Homer is racked with guilt and has to finally tell Mindy that he is confused by the conflict of his attraction to her and his sense of faithfulness to Marge.
Mindy assures Homer he doesn't have to do anything he doesn't want to, and it's up to him how far their relationship will go. After thinking about it, Homer decides to stay faithful to Marge. Mindy understands and accepts his decision, and she and Homer share a goodbye kiss before she leaves.
What the episode cuts out is a scene that happens before the trip to Capital City. Ned has told Marge that Homer called and confessed his attraction to a co-worker. Marge is upset, but decides she'll go to Homer, and confront him, and that, surely, some "special snuggles" will reconnect them.
However, as she walks to the bedroom naked, she see's Homer in his robe, his back to the door. She hears a female voice, and then spots Mindy on her bed. Shocked, Marge can only watch as Mindy is telling Homer not to feel so awkward at work, that the feelings are mutual, and that she has been thinking of him with lust just as much as he has been thinking of her. To demonstrate her point, Mindy slides off the bed and kneeling in front of Homer, slips his cock into her mouth.
When Marge see's this, she is furious. She knows this "hussy" is trying to steal her man. It wouldn't be the first time. She went crazy with jealousy when that woman Becky tried to seduce Homer. Marge recalls all too well how the men from the insane asylum shot her with tranquilizer darts, and put her in a straight jacket. She's not going to do that again, but will keep an eye on this Mindy, and she knows that despite temptations, Homer always comes back to her.
Homer, not always able to control his basic desires, and not always fast to think, just stands there as Mindy sucks him off. Still, he loves his wife and afterwards, tells Mindy she should leave before Marge catches them.
That night he is racked with guilt, and decides he'll go to work and tell Mindy they can't continue their affair. He writes a speech on his hand so he'll know what he needs to say. But that's when Mr. Burns sees them, and decides to send them to Capitol City.
That is why the kiss in the Hotel has even more tension, and why the conversation on the bed feels even more permanent of a break up. Homer and Mindy haven't just flirted, they've actually had a physical sexual experience together.
And now, as Paul Harvey says, you know the rest of the story.