You're a good friend. Here's a link to Partnership for Prescription Assistance....you may have seen their ads on TV. Montel Williams is their spokesman, and coincidently, he has MS and uses Copaxone.
Your friend can answer some questions on line and this program will help him find assistance for free or nearly free prescriptions.
I'm not sure how social security works with all of this, maybe some other folks will have ideas as to how to deal with them. Keep your friend laughing, exercising (as he's able) and finding things that interest him and give him hope. He's lucky to have you in his life-