First of all, you need more paragraphs. This gave me a headache to read.

Second of all, you need to realize this: you won't be able to help MS, AIDs, and other incurable disease patients any time soon, dear. Even if you did become extremely rich and donate millions of dollars to research, it wouldn't guarantee anything. Do not start a band. It's a terrible idea, and even if it does come through, it won't be the MAGICAL SOLUTION to all your problems that you seem to think it is.

If you quit school now, keep in mind that it will probably be even harder to find a job that can support both your mother and your friend. I don't mean to sound mean, but there's very little chance of your friend living to see a cure for MS. He's doomed. You can take care of him, but you won't be able to save him. Don't get any crazy ideas that you can change this fact.

Now, all things aside, the most important question is: what do you enjoy doing? Do you enjoy Biology? Do you have a passion for guitar playing? Forget about your family and your friend for just a moment. Indulge a little, be selfish! What do you want to do with your life? Only you can answer this. Don't let your family (or your friend!) answer it for you.