If you like, try this: He's gotten over his relationship with Faye. He hasn't gotten over his relationship with Faye ending as badly as it did. That's the crucial difference.
Let's tweak that: I agree Sven was never really in love with Faye—I suspect, for whatever reason, he's never let anyone that close to him emotionally. Remember that Sven's whole existence seems to revolve around not exposing himself in any way—lots of sex partners, but no lovers; writes songs that he knows are ridiculous, but never something he puts his heart and/or soul into (so far as we know); even the one friend we know of, Wil, is someone it's difficult to take seriously, and therefore I doubt they're that close, pre-Faye, anyway. (Note that after Faye, their relationship takes a decided turn when Sven tells Wil not to let Penelope go—before he'd probably have said girls were 'fungible.')
Sven shows no real signs of being 'in love' with Faye that I can see until after the break-up, when Sven gets jealous, which, I imagine, was a nasty shock. But prior to that, he holds her at arm's length, too, or at least thinks he is. It could be argued, I suppose, that Sven was/is in love with Faye and didn't know it, but I think not, although, honestly, it doesn't matter—what's the difference between a love you don't know you have and simply being strongly (for Sven) emotionally connected to Faye as a friend? I'll add I'm not sure Sven is capable of being romantically involved with anyone. Being involved with another person as a friend is, in and of itself, unusual enough for him; 'outside his box,' if you follow me.
This is why I suspect, both before and amid the sex, Sven found himself enjoying Faye's company (that's made pretty clear), achieving with her a closeness I think he previously reserved for Dora (the conversation he has with Dora at lunch and with Faye over her burrito seem pretty similar, for example). For whatever reason, Sven's made a habit of keeping people at a distance (again, I want to blame Mum and Dad, but have zilch evidence for that), but Faye got 'in,' first as a friend, and then as an
actual friend with benefits, as opposed to a 'mark' Sven had sex with, which seems to be his usual sort of encounter. I think that sort of relationship explains Sven's emotional commitment to Faye and his depression afterwards: Sven had a close friend, one who isn't 'stuck' with him because of blood ties, and he alienated that friend because, not being used to taking someone else's feelings into consideration (again, something Sven doesn't think he has to do for with his sister), he didn't. And since sexual intimacy meant far, far more to Faye, whatever she said, there's no way he sees of fixing it. Instead, Sven's forced to look at his behavior and perhaps not like what he sees. Worse, he may realize that Faye isn't the only one he's hurt this way—she's simply the only one he cared enough about to notice. Hence his 'dumps' and his comment to Marten about single girls.
This works for me because it also allows Sven to still be completely unaware of how he's effected his sister, because Dora's a whole other story—it's not like his sister could have been hurt by his self-absorbed antics, is it? (It may come to him in time, though.)
Finally, Sven's need for emotional distance also explains his various comments and actions that maintain said distance between himself and Faye during their relationship. That's the 'funny' part about the whole thing—even while he was getting closer to her, Sven thought he was keeping that precious distance, and didn't realize any different until after things went south.
I know, 'nother wall. But I've been good up til now, haven't I?