According to Jim Recap: Rules of Engagement
When Cheryl starts taking care of Jim because she's trying to make up for the fight that they had the night before, he likes it. He really, really likes it. But try as he might, Jim can't remember what it was that the fight was about. Don't think for a minute that will keep him from taking advantage of the situation, however. He's going to enjoy this for as long as he can. In fact, there is a wedding coming up, and he's going to use this to get out of it.
So as the big event approaches and Cheryl is getting antsy because she wants him to get ready, he pulls out the big guns, telling her that he still needs some time to come to grips with everything and to make sure that it's all behind him. Frankly I don't get how she still buys all of this. I mean she has been married to him for more than a decade at this point. But she must have been feeling awfully guilty, because she takes his excuse that he was talking to Andy all day at face value, and heads off to the wedding without Jim.
When Cheryl gets to the wedding and asks Andy about it, however, a different story begins to emerge. That's when things get a little foggy, however, because Andy rapidly shuts up when he figures out that Jim hasn't told her a thing. A massive wedgie from Dana gets Andy talking, and pretty soon Cheryl knows that Jim has been faking the whole thing, just to get out of the wedding.
After they all come home, Jim flips over to the game and acts as if he has put the whole thing behind him - easy enough to do, when he doesn't have a clue what it was - and that's when Cheryl lowers the boom, telling him that she needs to hear what it was that hurt him most. And that, in turn, is when he gets busted.
