I disapprove of this going back to Sven because he's sorry. Sometimes you just have to cut toxic assholes out of your life, even if they are family.
See, I agree with this sentiment, at least in theory. I've luckily never had to do such a thing with family, but there are some friends I finally had to cut ties with when I realized just how toxic they were.
My only quibble is that I don't see how Sven has been especially toxic. Has he been a jerk at times? Sure, but no more so than some other folks have been in the strip (and less than some.) He's also, like other characters, made efforts to change those things about him that are toxic, with varying degrees of success.
I'm not going to say that he's even a "good" guy. I mean, "cheating" on Faye (even though they weren't exclusive) was a super-douchey move. But that's not the straw that breaks the camel's back. It's him going up to Faye and confessing his "love." Even though he acted completely cluelessly there, it's never quite clear that he even knew she was in a relationship at that moment, and
some of what he says during that conversation is evidence that he's at least trying to improve himself, even though he's just frankly terrible at it and is fumbling awfully (the rest of it is, yes, him being a clueless dipshit.)
But this conversation is the horrible sin that causes Dora to "realize" that he's a toxic person? When any number of other characters have fumbled their way through their development, often putting their foots in their mouths (or inadvertently stepping on others with said feet) yet treated with patience and acceptance?
I think Dora's stance here is less about Sven being any more toxic than anyone else, and more about her. I've never been one of the readers to think of Dora as being a particularly bad person, but in this case I think she's just too close to the situation, and this has more to do with her own unresolved issues with her brother than his being especially "toxic."
So, tl;dr: yeah, I'm welcoming this development. If anything else, it will give Dora an opportunity to deal with an unresolved issue. Worst case scenario, maybe we all learn that Sven really is as toxic as Dora feels, and her stance is justified. Best case: they both grow as people and learn some things about dealing with their issues that leaves them in a healthier place.
(But again, yes, I do agree that sometimes one has no choice but to just cut ties for one's own health. No one should be forced to stick around someone toxic just because they are "family.")