For example, the childhood friend had a shitty life and all, but she also had two children. Couldn't you argue that living for those children and trying to make them happy would make her life worth living? But we only saw her life as "depressing". Same thing with the MC, arguably. Just because he didn't had any "accomplishments" does that really mean his life just wasn't worth it? Granted they said he wasn't happy (in the present or "future"), but it's not like you need to find "the thing" that makes you happy to make your life worth it. It's fine to try finding meaning in ordinary things like simply listening to music, reading books/manga, etc. I'm sure he probably had small moments of happiness in his "future" life even if it wasn't overall positive, so who's to say it wasn't a life worth living. Although it's hard to argue against the kind of omniscient prediction they pulled, so I digress.
Another factor that somewhat rubbed me the wrong way, is that the story develops straight from "your life is shit and nobody loves you" to "here's a cute girl your age who is nice, understanding and in a similar situation to you, also just by talking to her you will be the nicest guy she ever met and she will fall for you". Ahem, of course that's just my perspective, but it was hard to swallow what the story was trying to convey when, in practice, all positive development could only have happened because the MC was "lucky" enough to find the perfect person to stay by his side. I do even go as far as saying it's unhealthy to make depressed people (or anyone in a similar situation to the MC) expect finding someone as "perfect" for them as the FMC. At least I expected a more "you need to make your dreams come true instead of just waiting" approach, and while I think they tried to do that, I couldn't feel that at all because the FMC is just way too "perfect" of an addition to his life (always by his side, always supports him, lonely just like him, and conveniently the same age as him and single). Anyway, maybe I'm just nitpicking here, and it was still a good work of course, but I think it could be better.