Firstly I would encourage you to see an counselor. A good counselor will not only affirm that you are indeed not a bad person (as you most certainly do not sound like one) and will help you get to the root of the specific causes of the disconnect between who you feel you are and who you want to be. That you are concerned about and have chosen not to act on your negative feelings says a great deal about your good moral character.
However, your description of yourself sounds very similar to how I have felt at times during my life including relatively recently. I also often feel like I live with a “pitch black sense of humour coping mechanism that’s gone to far”. I am 57 years old and hope that you will not wait as long as I have to get to the root of your discontent. I will share my story just in case it sheds any light on what you are experiencing.
The root of my disconnect is that I have been overly nice for way too long and have built up lots of resentment inside. Having ADHD has resulted in lots of uncomfortable interactions with co-workers, friends and family and as a compensating mechanism I have tried too hard to be exceptionally nice and helpful. I’m naturally a nice enough person but not as nice as I was trying to be. As a result I felt taken advantage of and unappreciated which eventually turned to anger and negative judgments about the people around me. What has surprised me was is all I was conscious of was the anger and the rest was residing deep inside (and I have had lots of counselling and considered myself as being pretty self aware). I’m now learning how to have appropriate boundaries around being “nice” and to balance my needs with those of others. My 18 year old daughter has also had counselling on the same issue as I had brought her up to be overly nice.
My one encouragement would be to not be so hard on yourself. Life is not easy and life with ADHD has its own special burdens. I have found Acceptance and Commitment Therapy useful in helping me to move past the pain which was created by having undiagnosed ADHD into a life driven by what I value.