I'm not going to judge your tastes in storytelling, but it sounds like you haven't been exposed to anything but the blandest of stories in the past. Most good literature doesn't feature purely happy endings (and if they do, it's typically because the story has made itself worthy of such a thing through the telling, something that doesn't happen often). The best stories are usually bittersweet, and that's how my stories lean too.
The sad or unresolved parts of this story are there to add weight and consequence to a game that relies heavily on actual choice. If the consequences weren't there, the choices would be meaningless. And a 100% happy ending for a character who's been behaving like a jerk, even if the narrator (himself) doesn't call him out on it, would hit a false note.
You can get an almost sickeningly sweet happy ending from this game if your choices support this, but most players are likely going to end up with something bittersweet.
Additionally, you might find the endings short, but that's also highly deliberate on my part. It's all too easy to linger too long after the climax of a story, at which point the audience is already spent. Most stories are best served by quickly wrapping up once the climax has passed, and this is certainly no exception. The epilogue is almost too long as it is, and extending it would add nothing of value, in my opinion.
To circle around to the beginning again, it really sounds like you need to broaden your exposure to literature (or entertainment) if a story like LLtP bothers you in how it resolves itself. I'm not going to sit here and claim that my storytelling is perfect, but it is definitely not something that happens by accident or by stumbling into it without purpose. I know what I'm doing and what I want to achieve, and I didn't cut off anything because I got tired of it. This is the story I wanted to tell.
Thank you!