Not an Isekai, but if you've ever watched Princess Tutu, that is entirely about changing the story as written to pull a happy ending out of a planned tragedy.
So, out of curiosity, how would Freddy manage to skirt the whole "being married already" thing?
I've heard of that title, and I've heard good things about it, but honestly I've never given it a watch. Maybe it's high time I changed that.
Honestly, I haven't put too much thought into that aspect of his character just yet. I mostly added him as a way to include a crack ship that I really like but don't generally see a lot of. I may tweak things a bit so he's less morally reprehensible and more just obnoxious.
Maybe he and Bethesda aren't actually married yet. Freddy could have had his eldest child Seviathan with Wife 1, lost or divorced her, then at some point in the future meets Bethesda and has Helsa with her. Problem with doing things this way means that Helsa ends up way, way younger than Charlie which means no comedic headbutting between the two.
Charlie: I'm having problems with this mean queen alpha bully bitch. Alastor: Kill her. Charlie: ...Not doing that. Alastor: I don't know why you keep coming to me just to shoot down my suggestions.
Or this could just be something he and his wife do from time to time. Get in an argument, 'break up,' start pursuing other people, and then reconcile and fall even more madly in love than before. A super fucked up dynamic in reality, but a kooky eccentric rich people thing in the context of the story.
Live Alastor reaction:
Or maybe he's just a dick who doesn't care about betraying his wife. I feel weirdly guilty about considering that route though, since we haven't even met the guy in canon and here I am slandering him. At the same time, this route could enhance more of the 'drama' in 'dramedy.' As a high ranking noble he probably can get away with having a number of affairs as long as he's not flaunting them.