>>802655I'll second everything Asano wrote (yet to read DeDeDeDeDeDe though) like Nijigahara Holograph, A Girl On The Shore, ect. ect.. Even his more upbeat works like Solanin involve some deal of suffering. Berserk is another good one I hear (waiting for it to finish never ever before rading). Devilman's a sublime work on the suffering of empathy in the face of an uncaring world, amongst other things (and you need to read it anyway), and the related sequel works like Devilman Lady and Violence Jack (and prequel shit like Demon Lord Dante) are all somewhat similar in thematics.
To give my own recommendations: Homunculus has a fair bit revolving around suffering and how people need to move past things that happen to them, and Ressentiment is a very good (if very depressing) work on the pain related to secluding yourself from the world.