Hi Shannon,
I'm not sure whether you realise that the Answerbank is based in the UK. (The timing of your post, together with some words in it, suggests that you're on the other side of the Atlantic). So you won't get many immediate answers because it's approaching 5am here. If you'd rather post on a US-based board, try one (or both) of these:
http://www.answerbag.com/
http://answers.yahoo.com/
However, families and relationships are basically the same throughout the world, so I'll give you my opinion:
You say that you want to better your son's life. Ask yourself what he
really needs right now. I'd suggest that the answer isn't 'money'. It's not 'more toys'. It's not 'smart clothes'. The two things he really needs right now are love and a secure, stable family environment. Even though your father and grandmother would give him all of their love, it could probably never match what he's come to expect from you. Equally, children need security. Your son is used to living with you and expects you (and you alone) to be there when he needs you. Your father and grandmother could never truly replace you. Further, as well as the disruption to his young life that your departure would cause, there's the possibility of him getting caught in the middle of a 'tug-of-love' struggle between your father.grandmother and your son's father. That's going to put him through a great deal of stress and confusion, which would only be made worse when you reappeared, and then left again, during your leave periods.
If you leave your son (even with the best of intentions) you'll be stealing from him. You'll be stealing his security, you'll be stealing his confidence and, worst of all, you'll be denying him the love of the one person who's most important to him.