Amanda:
All you really need to tell the 9 yr old right now is that mommy has some problems and needs to go for 'treatment' and NO it's not cancer. You can tell him you will be gone for a while (don't say exactly how long, but you will phone him and send him cards and letters.
Buy yourself a long distance card at Wal Mart, Walgreens, whereever they have them by you, they are refillable too, that way you can still be in contact with him.
Above all.....................................focus on you. This is for you, for a better life. Learn all you can, get all the tools you can. This is the MOST IMPORTANT THING you will do FOR YOU!
In time, using the tools you will garner, the 'wreckage' of the past will resolve itself, please focus on TODAY.
I will keep you in my prayers.
Love and hugs,