Advice: Too Old to Switch Gears?

I'm a 42-year-old full time working mother of one. I want so badly to be a nurse but it would take at least six years to become an RN. I don't know if I can handle all the duties I already have now. I am married, and not particularly happily as my husband over-medicates with pain meds for the buzz factor. He often acts irrationally and gets drunk. I can't take it anymore but I cannot afford a lawyer and of course my top priority is our son. My husband is a great father and loves our son; he has voiced his fear that I will take our son, as I did twice in the past—one time when hubby was not home at 3 a.m., another when he accused me of stealing his meds. I feel I'm STUCK. I do the same thing every day: get up, go to work, hubby goes to work, I come home, TV is on, I turn it off for my son's sake, cook dinner, clean a little, play with my beautiful son, hopefully get a little walk in, then go to bed. I have no friends who come over. I feel so empty and lost.