It sounds like your boyfriend may need some counseling to help him cope with how the accident has changed his life. This trauma has affected not only his quality of life, but you and your son's as well. Its not fair to you when you are there being supportive and helping as much as you can.
See what you can do to get him some counseling and look into therapy options that will help him become more independent. Don't compromise your own happiness. Ultimately, you can not continue to remain in what seems like an abusive relationship. I know you feel bad about what's happened to him, but you may have to make some tough but necessary decisions. You and your child are worth it and deserve to be treated with love and respect above everything else.