So here's the thing: whether or not he was overindulging in substances back then, he was always the same person inside.
He didn't develop a creepy corrupt soul in the last 3 years, and he didn't start being a sneaky cheat then, either. This is a kid who thought was funny and edgy to write poems to read in creative writing class about the school burning down and who had a kill list - which he still thinks is both funny and cool, and he has always liked the off-putting effect that saying that has on other people. He's a spaz who mistakes disturbed for edgy. Like really, he was and is an unlikeable person, not because he's "too edgy" for vanilla people, but because he is dark inside. Not a grand, sweeping, Romantic darkness, either, but rather dark in a small, shriveled, shallow way. And it's been catching up with him.
He's pitiful in the way he constantly does mental inversions to try to turn being a petty midwit misfit into being some kind of iconoclastic genius his enemies are just too dumb and too ordinary to understand. He's the guy who fell down a well who unironically and triumphantly proclaims himself king of all that he surveys and who would rather trick other people in there with him into killing each other than to work with them to figure a way outt...and cackle at how stupid they are.