Apologies for interrupting, but there are a few things in this post that I'd like to address. Spoilers for the entirety of Super Dangan Ronpa 2 under the cut!
I addressed a lot of this in my personal thoughts on what Komaeda said already, but I'll try to elaborate a bit here.
First of all, Komaeda's life expectancy of "half a year to a year" was an estimate, and those can be off - quite possibly by a fair bit, as there have been people who've outlived their original life expectancy by literally years. The thought of him potentially living a few years past his original life expectancy might be strange at first, but it's far from impossible. Add Komaeda's luck, which has a track record of causing a lot of improbable things to happen, and it's even more likely.
Aside from that, his life expectancy was based on two conditions. Of the two, malignant lymphoma is more likely to be fatal... but it's also treatable, and since we do know that Kibougamine has medical facilities, it's not impossible that he might have received treatment for it during his time there.
That would leave his frontotemporal dementia, which isn't curable. The average life expectancy for that is anywhere from two years to a decade, and it's not unheard of for people with it to potentially live even longer than that if it's a slowly-progressing variant. Komaeda does exhibit a large number of the earlier symptoms in the game (a few samples are mentioned in the link near the start of this post), so there's a good chance that he does, indeed, have a slowly-progressing variant of FTD.
Hinata's remark is definitely NOT the game hinting at anything. It's literally just one of his thoughts, colored by his own suspicions of Komaeda - it's pretty clear that in the main story (and only the main story, as they're on pretty friendly terms in Dangan Island), Hinata has trouble trusting Komaeda after the events of the first chapter, and this same distrust leads to him completely misunderstanding him a few times (most notably in Chapter 5, where he gets Komaeda's actual intentions so horribly wrong that Monokuma outright mocks him for it). If anything, that line just shows that Komaeda's line about the book he read threw Hinata off - prior to that, he does actually seem to believe Komaeda, to the point of starting to reconsider if his actions were really unforgivable in light of what he just learned.
Hinata also definitely did not recognize the aborted confession as such - the student ID's recap for the event makes that pretty clear.
The "lie" here, if anything, would be Komaeda's attempt to paint what he told Hinata as a lie, and that's more him being evasive than anything.
If there's one thing Spike has been highlighting a lot, it's that Komaeda is actually a pretty honest person. The game itself already establishes that to some extent: the Despair Disease, which seems to invert the affected person's most prominent personality trait, turns him into a liar. His internal narration when we play as him in Chapter 4 corresponds perfectly to the things he says and does. In Dangan Island, there isn't even a single instance of him lying or being malicious in any way.
Extra materials and commentary make that even clearer. Ogata, his voice actress (who notably influenced his character a bit), considers him a honest person. Komaeda's chapter of the Dangan Island manga (1, 2, 3, 4, 5, 6) showcases his helpful nature, which is also mentioned in the Setting Material Collection. His official profile notes that he seemingly holds no ill will, with more recent versions of it (such as his profile in the September issue of Famitsu) removing the "seemingly," a change that's retained in Jin's description of him in the mini-novel included with volume 1 of the anime. His own spinoff manga, 超高校級の幸運と希望と絶望, shows the same overlap between his thoughts and the things he says/does as his segment in Chapter 4 but for the rest of the story, and clarifies a lot of his actions a bit more than the game itself did.
There aren't actually a lot of instances where Komaeda definitely lied, and they're all out of necessity. In Chapter 2, he lies to gather the people mentioned in Twilight Syndrome's credits at the airport, which he admits and apologizes for - but that was literally necessary for the investigation at the time. In Chapter 3, he "lies" about the rope being unimportant - it was unimportant at the time, and in addition to that, he and Hinata were having that conversation in front of Tsumiki, who was the person he suspected from the get-go. Pointing out the rope's potential importance right away could have led to her making excuses, which would've made it much harder to actually convict her for her actions. The last is in Chapter 4, about the contents of the file he received - the last scene of the chapter makes it clear that he lied because he didn't want the others to be burdened by the truth (aka their status as SHSL Despair), and he's pretty clearly surprised that nobody called his lie.
"Lying about murdering people before"... I'm not sure what you're referring to here. If you're referring to how his luck caused the deaths of people around him (such as his parents), that's not a lie; that's all but outright confirmed in the Setting Material Collection and flat-out confirmed (twice, now) in his spinoff manga. If you're referring to his line about how he's going to commit a murder when Teruteru confronts him in Chapter 1 - mistranslation. The original line is a question, giving the line a "that's what it seems like to you, doesn't it?" sort of tone. Even if we ignore that, though, he was trying to get himself murdered so at least one of the students would have a chance to escape the island, so regardless of how you look at it, that wasn't a lie.
And as for his plan in Chapter 5... I think you may want to reread that chapter again. His plan wasn't "let's get everyone killed for the sake of hope." It was "try to have everyone but the traitor executed because we're SHSL Despair and our existence could threaten the world." Tsumiki already relapsed, after all, and Owari got pretty close. The Future Foundation had the same view - the remnants of SHSL Despair need to die, or otherwise the Incident will continue. That's why Naegi got in trouble with them for sheltering the remnants instead.
It's still a pretty morally questionable plan, but he definitely wasn't trying to get everyone killed just for the sake of hope itself.
Aside from emphasizing Komaeda's honest nature, there's been a fair number of extra materials that made it increasingly clear that Komaeda wasn't lying about anything - not about his past, and not about his conditions.
The very first chapter of his spinoff manga confirmed his story about the death of his parents, which the Setting Material Collection also heavily hinted at, and which the game itself hinted at with his reaction to the aircrafts at the Jabberwock Army facilities in Dangan Island.
The most recent chapter had a nightmare sequence that also showcased a few things - the death of Komaeda's parents is included here too, albeit in more detail.
It also showed the kidnapping, which was already hinted at in-game by his negative reactions to the gag ball and to movies with serial killers in Dangan Island.
And, most importantly for this post, it also showed the moment he received the diagnosis for his conditions - something the game itself hinted at with his behavior (which matches up very well with the earlier symptoms of frontotemporal dementia), and by Kamukura's comment about Komaeda having "the stench of someone at their life's end," and which the Setting Material Collection also supported by not-so-subtly hinting that the color of his hair and his sickly pale skin are likely the result of poor health.
While I can agree that it's probably better not to assume he's telling the truth just because he said so, there's a lot more pointing toward that conclusion than just his own words, and most people do seem to take more than just what he said into account. Claiming that those who choose to believe he was being honest didn't read the game fully or properly is... kind of impolite, to be honest, especially since you seem to be neglecting - or willfully ignoring, in the case of the spinoff manga - parts of the canon yourself.