That's a standard jealous reacton. He reacts that way because he's HURT.
Things to remember:
Sven WAS a manslut. He proceeded to make very significant lifestyle changes based almost entirely on Faye's sayso (I was going to say "toungue-lashing," but that came later). Why did he do this? It's become clear that he is attracted to her in a more than physical way.
It isn't reasonable to expect him to change so drastically overnight and never lapse. It's not uncommon for alcoholics, for example, to lapse, early in their attempts at sobreity. Even during his lapse, it was clear that he didn't want to be doing it, at least on some level. That is, he knew what he was supposed to do, but was unable to curb his desire to do the opposite.
Likewise, we find Faye hurt for many of the same reasons. She actually likes Sven more than she intended to, or perhaps realized. He was one of the few men in her life that didn't treat her like a delicate flower. Further, he did make major life-changes for her. She couldn't have failed to notice this, even subconsciously.
They are, however, now facing some serious denial issues. Sven is wondering if it was worth it to make the effort to change, especially if the person he was trying to change for was just using him for sex, the very thing she berated HIM for. She's hurt because she's wondering if he was really trying to change. However, they're both trying to deny that they really felt anything, and are refusing to talk.
If they were simply honest with each other, they might actually establish a healthy relationship.
Just my two cents...