I didn't get the impression that Sven was acting manipulative, more that he wanted something and expected it to be handed to him. After the 'date' he had with Hanners, I find his approach with Faye at the very least a character regression.
Yeah, I read it less as 'I'll make Faye think Angus is bad and I'll save her and trick her into liking me muwahaha!' and more 'but that's how it ALWAYS works, isn't she supposed to like me now?' which while
dumb is not manipulative.
And he is supposed to be smart. Even if he doesn't have much of a sense with actual relationships (as evidenced), being able to write songs and play music is a skill, even if they're terrible (especially since they're consistently terrible- it's not like he's failing at writing 'serious' music), breezed through school which, while showing lack of effort, shows intelligence of some kind and that he must absorb information fairly well, and he has been decent at reading both Faye and Hannelore (and probably Dora and others that I'm not specifically thinking of) in the past. So while his kind of assholey, very romantically inept behaviour is explained, the very degree of it in this last comic seems really off.
Of course, shitty emotional intelligence that isn't just being joked about or off screen, apart from fleeing Genevieve, is displayed when Marten is trying to talk to him about Dora (after the underwear thing, which I can't find a link to on the wiki). But only at first, then it gets a bit more human and he talks about Dora's previous guys.