Thanks for your question.
I'm sorry to hear about what you've been going through with the father of your son. While adhd can cause a lot of difficulties in concentration and focus, it doesn't make someone abusive or explain the problems that you've described. I certainly respect your desire for a family unit and what you are willing to go through to achieve that. In order to get to that point though, it is important that you and your partner are both working towards that, and that he is willing to put in as much effort as you are. That seems to be the point where a lot of the problems are occuring.
Forgiveness is certainly important, but it also may not cause him to change the way he treats you. If he is not willing to get help and is unable to take responsibility for his role in these problems, that takes a lot of the control out of your hands. It is understandable that you would not want to be alone, but the decision to stay in this relationship may be a decision to continue to put up with his behavior if there are no signs of remorse or willingness to work on his problems.
I know that you said that you've tried 'everything' and the tendency is to think that there is something that you can do, or something that you can change, which would cause him to change. Unfortunately that is typically not the case with people who are abusive. They need to get to a point in their lives where they recognized it and take responsibility. Some people get to that point, others don't. While I understand the fears involved in ending this relationship, it's also important to consider the example it is setting for your son, as it will effect the way he approaches his future relationships. If there is no end in sight to this or no signs that he will change, it's most important to consider the health and emotional safety of the family unit that currently exists.
I definitely wish you the best with this, and if there's anything else I can do to help please let me know.