First of all, if Bonnie is feeling unfulfilled in their marriage, then she has a right to end it. This whole idea that couples should stay together just for their kids is a bad one, if you ask me. You know what kids like? Parents who aren't constantly bickering.
Second, we have already been through this story, and it was a lot funnier the first time. The episode where Cleveland's first wife Loretta cheated on him with Quagmire is outstanding. And Cleveland's emotional range in the episode was impressive. By comparison, Bonnie and Joe just kinda sit there staring blankly.
You know you're in trouble when the script forces a character to literally say, "I want to have an affair."
And finally, so what if Bonnie wants to have an affair? If she doesn't want to actually leave Joe, if she just wants to get some on the side, I really think that Joe would probably be okay with that. I was already under the impression that they had an open marriage. (I forget the set-up, but I'm recalling a scene where Peter is awkwardly lured into having sex with Bonnie, while Joe watches from the darkness on the far side of the room.)
Without some kind of investment in the main storyline, all you're left with is a bunch of standard issue sitcom shenanigans. In the B plot, Peter gets freaked out about the possibility of "goat flu," so he pulls Chris and Meg out of school. His attempts to home-school them in the garage go about as well as you'd think they would.
The episode's lowest point is when it makes a surprisingly tired joke that relies on stereotypes that black people are bad at math, and Asian people are bad at driving.
I was also a little baffled by the "Joe is Stan Smith" gag, because I identify the characters with their voices more than their physical traits. (But it was hilarious to learn what a terrible singer Patrick Warburton is. I guess we won't be getting any power ballads from Brock Samson any time soon.)
The "Ferris Bueller" scene was pretty great, mainly because none of the characters acknowledged that it was a Ferris Bueller scene.
But for me, the high point was the cut-away gag to "the gayest music video of all time," the 1985 Mick Jagger and David Bowie cover of "Dancing in the Street."
Rewatching the video for the first time in at least 20 years, I was surprised to discover that Peter was not wrong. I mean, maybe not OF ALL TIME. (The video for Lady Gaga's "Show Me Your Teeth" comes to mind.) But still, even aside from the outfits (the less said about which the better) the sexual tension between Bowie and Jagger is phenomenal.
Watching the video as an adult, I totally believed all the rumors. (Particularly since the song isn't about sexual tension at all. It's not like the lyrics call for them to stare intently into each others' eyes.)
As the video ends we cut back to Peter, who solemnly intones, "That happened, and we all let it happen." Frankly, I'm still laughing at that.