A.B.
You do sound exhausted. You're not selfish - you've done a great thing by breastfeeding your children! I remember feeling guilty about those "I've been nursing forever" feelings, too. I'd suggest that you try to shut out everyone else's ideas of what you "should" do, and go with whatever your instinct is telling you is best for your family.
Will your son take a bottle at night if someone else gave it to him? If so, you may be able to both wean him and have him learn to sleep through the night at the same time. Once you're getting more sleep, you'll be able to spend close time with him after work that doesn't include nursing.
My son was a 9 lber, too, and I remember thinking he'd be in college before he quit nursing. To this day he still craves physical contact from me, but he did wean without too much trouble when he was a toddler.
Is your son eating solids so that he's not so hungry during the night? I'm certainly not a pediatrician or nutritionist, but I should think if you're going to start milk in a couple of weeks anyways, it wouldn't hurt to start now. Maybe I'll get blasted for saying that - it's been quite awhile for me and I'm out of the loop as far as the pros and cons of cow's milk. I'm sure you know to make it a small part of his total nutrition. I just hope you can get some quality rest soon. You will, and you'll have fond memories of the great start you gave your children. And you can pretend to hold it over their heads when they're teenagers. "I didn't sleep for two years!" Just kidding. Sort of. ;-)
Best of luck to you.