Dude I feel exactly like you with the difference that for me, Alvy is literally my favorite character. I'm also very sad with the ending...
(In my dream world, Alvy's route kept going and now it won a frickin Oscar and a nobel prize)
While I agree that the ending was... a lot, I also think it did need a rather sudden and extreme ending, to really hit the audience with the point that that is the end of his route entirely, among other things.
Obviously, Alvy will still be around, and may return in Scribbles' route or Chapter 2; he will still be part of the story, just as Therium is a constant annoyance presence, even though he's no longer the focus of the route, but for one reason or another, the author has decided that this is where his route ends. My assumption is it's because he's such an integral side character that actually having a route for him would (most likely) continue to completely change the story from the way the VN is now—it would no longer be focused on a fantasy romance academy story.