Shonen no Abyss has a good a premise and potential to be a deep story that covers dark themes. With some great artwork, it really really had the potential to be good. Sadly, the execution is not the best.
As the story goes on things get wayyyy too convoluted for it to be interesting. Being hit with plot twist after plot twist, some which are completely unnecessary. There are no safe grounds in the story, promises are made then broken a few chapters later.
And finally, no progression, the story has followed this same loop multiple times... main character is sad, main character and other character have sex, other character breaks down (or plottwist), false promise, and then repeat.
The MC lacks a discernable personality, he changes to the benefit of the plot, he lacks consistency. At times he is a complete pushover but when the plot requires it he isn't. He wants to kill himself, but when the plot calls for it, he does not.
The teacher is insufferable. Anytime she drops any wisdom about how adults are I can't help but roll my eyes. Which may be the author's intention and if that is so bravo. However can't help but feel these lines about how adults function were not written to be criticized, but rather written to be "deep" but instead it just comes off as really juvenile.
The other characters however have interesting personalities.
To conclude, do I recommend you to read this manga? No, it sucks, unless you like reading trashy manga. If you want to read something dark and kinda deep, read Killing Stalking.