I can't help much but wanted to add that YOU are the parent and it is your job to make sure your son has the education he needs. That being said you have a lot of options -- others mentioned some of them and here are a couple more...
homeschool -- if you do research on the internet there are TONS of resorces for adhd. Even if you don't homeschool him the resorces can help you understand how he learns and how to talk to the school and how to teach him at home (with the schools help).
add nature and play to his schedule -- nature calms and focuses adults and children. Outside play will help his body work for him instead of against him. Limit screen time -- they make adhd worse.
You say he is a loving and caring soul -- that is WAY more important then if he does "great" in school. Make sure he knows you are on his team and believe in him. School is important but LEARNing is more important. Have him prove he has LEARNed the subjects even if he doesn't do the homework. Have him TALK to you about them or e-mail you or text you about them. Sometimes homework is just busywork and NO ONE likes to waste their time. Maybe you can prove to the teachers he has learned the subjects in a different way then traditional homework.
You say that he wants you to do all his homework for him... does that mean he KNOWS the stuff but wants you to write it out? Or he wants you to read the book and do the book report without him? In a job he will not have you to do the work BUT he is only 13 and his job is learning right now -- help him learn as a team.
If decision making is the main problem then work specificly on that. For example do word "problems" with him in the car or something. Tell him about a situation and give him choices to pick from. Kind of like those old books about choose you own adventure. Then after he gets those do open ended situations. Ask him why he would do that, make him think through situations before (and after) he has to face them. Guide him to the "right" way through questions.
I will pray for you-- parenting is hard at whatever age they are at. YOU can do this and so can he. Make sure he knows that you love him.
GOD bless.