Hello. I'm not a parent with a child in your situation. I'm a child that has gone through years mental health issues and I have a master's in psychology. First, your son loves you. It sounds presumptuous, but he is hurting and so he is lashing out. It doesn't mean he doesn't still love you or need you, and I'd suspect he hates that his life is causing you stress and pain.

I was a straight A student and athlete in University when I had a breakdown. I became paranoid of even the fumes coming through the vent in my dorm room. I was a residential advisor at the time, helping others adjust, while I was silently falling apart. This started after major losses in my life - divorce and death of loved ones, but in all reality, due to trauma during my childhood, I had struggled with feelings of being alone, or lonely, even with others.
Eventually, I reached out for help after a drastic attempt to take my life. It was a pressure that built up in me so great that I couldn't handle it or cope. I'm now older and looking back. The only thing that my family or friends could do to help is simply be there, listen, and try to be as understanding and supportive as possible. It may be you can't reach him through rational means and common sense conversation -- and definitely not with the old school "pull yourself up by your own bootstraps" speeches. My Dad was strict, military, and mental illness was simply weakness. I've since learned that's not the case at all.
What children experience during developmental stages of brain development does impact brain structure. Trauma can permanently change the brain - abuse, verbal and physical, stress, and so many things affect brain development. Sometimes, the trouble doesn't fully present itself until later in life. It may be a type of survivability where we are impacted by trauma and can only cope with it years later as adults. Children, although people say they are resilient, are sponges and the brain wires itself to survive.
Obviously, I don't know your son's history, but if he had a difficult time as a child, tried drugs, or other unhealthy coping mechanisms, it only compounded and complicates life when we try to fit into society as "normal" functioning adults later.
I would recommend continuing to just love him and listen to him without criticism or judgement. He is probably trying to fight through an inner struggle that he may not even be able to put into words.
Also, please don't only assume that depressive or irresponsible behavior is simply something a pill will remedy. I've tried so many medications and very few helped. One thing that is good is genesight therapy. It's a test that a primary doctor can order that will let him know what medications will work the best with his genetic makeup. That way he won't feel like a test subject while cycling through ineffective options.
I was recently diagnosed with Frontotemporal Dementia. This illness presents with behavioral problems, and it can be mistaken for mental illness. I was diagnosed bipolar (among other things by therapists who just really want to put a label on behavior and send you off with a pill). It may be an MRI of his brain would be helpful to see if anything more is underlying his emotional and behavioral difficulties. A neuropsychologist might be a good option for him. Frontotemporal Dementia can start at a younger age. I'm not saying this to say that's what it is or to cause you further concern, but to let you know there can be more going on in his brain that is causing behavioral changes, and it is worth investigating.

I hope he comes around soon to you to comfort you and let you know he loves you. Please realize that depression can suck you into a completely warped and self-absorbed world where you are simply struggling to survive each day, so it becomes harder and harder to be thoughtful of the needs of others because it feels impossible to add more to the load your already carrying. I'm not sure if I should send this to you because it's not really my place, but as a child whose been through hell, I can say I never stopped loving my parents. I just hated myself, my thoughts, my struggles, my anxiety, and the paranoia. Nobody wants to live that way or be seen that way, so we withdraw. However, your love is a strength to him -- even if he doesn't show it. It's not fair; it's difficult for both of you. Just please hold on and be there for him -supportive, kind, patient, and without judgement. I'm a Christian, so I will say pray for him, don't quit on him, it's a rough road, but you can make it through in time. I hope in some way this was helpful.