Very good points and I can definitely see that. Yeah, and it seems that they all forget Catherine was once a stripper and turned her life around. You just can't judge a book by it's cover. But in the end Ellen was bad news anyway and Nick was probably thrilled to some point that she was because he knew it would not last between Greg and her.Then, in A Kiss Before Frying, Nick encourages Greg to date someone because Nick wants to help Greg get over Nick. For whatever reason, Nick feels like it's the right thing to do because he wants Greg to be happy. Instead, he realizes that he can't actually stand the idea of Greg dating someone else, so he uses Ellen's profession as an excuse to encourage Greg to end it with her. I still find it hard to believe, especially based on past events on the series, that Nick actually disapproves because of her profession. Doesn't it seem kind of ironic that she has almost the exact same profession that Catherine used to have? Which means that he has to be encouraging Greg to end it with her for another reason -- because Nick doesn't want Greg to date someone else.
Even the most together couples I know IRL have had break-ups. Sometimes, it just happens. The real test is whether they get back together. And, as far as I'm concerned, Nick and Greg definitely got back together.
ETA:
I have to say that I actually really liked the episode.
But I can see Greg eventually going back to Nick for comfort since he was pretty hurt by how the whole thing turned out.