Of course, Nancy's not the homewrecker -- that would be Jack, who wasn't wearing a ring and who fucked a lady not his wife -- so instead of meaning anything it just means that A) This is a guy we probably could have stayed with for awhile, and looked at the whole time and had lots of sex with the whole time and B) That at least, as Nancy admits later, he got the job done.
At this point, many things happen. Everybody shows up for the baptism to hear Jack's wife losing her shit, and then Pastor Randy comes out to calm everybody down, but then Keith, wonderful Keith, tighty-whitey Keith comes out of his trailer screaming, "I'm not saved! I did meth today! I'm so high! I feel awful! It's great!" Sugarpop comes after them in her housecoat, and everybody is screaming, and finally the Newmen -- I mean it turns into a real riot scene, with everybody calling them fakers and liars and stuff -- just pile into the van and scream off into the morning light.
I can't remember the last time Nancy having sex was a direct result of her deciding to have sex. I mean, she's had lots of sex -- most of funny, some of it rapey -- but the only time the storyline was "Nancy needs to fuck somebody or she risks dying on the vine" was that awfully touching S1 episode with the vibrator and the sex tape where you cry at the end. So probably if Nancy really needs to have sex, she should go ahead and do it -- get the job done -- because that stuff tends to squeeze out other parts of the toothpaste tube if you're not careful, and vice versa of course.
But to go from hating the trailer ranch so much that she ran, to having this crazy intense hot sex with this guy and being okay with it, to the face she's making now -- beaming, in her big black bug glasses, yelling and empowered about all the hash they're going to make -- you have to wonder if she didn't enjoy the morning after just as much. That sexy dirty hangover feeling, as they drive away. The fact that Jack will survive her. The sick little smile that slowly fades with the song on the radio ("Did you tell her what we did?") and she comes back home to her little van: To movement, and isolation. To the feeling of flight.