I am sorry to hear you've been going through such hard times. You'll find a lot of support here.
I don't know you, and so I have no way of knowing if what I am about to say is relevant. Feel free to dismiss every word that follows.
But after I quit drinking, I gradually discovered that alcohol had cast a pall over every aspect of my life. I had a ton of resentments—my relationship with my dad, my ex-wife, the demands placed on me at work, the guy who cut me off in traffic on my commute home... on and on. Gradually sobriety shifted my perception, and helped me focus on the half of the glass that's miraculously, wonderfully full.
My dad and my ex still do the same things as before, but I've accepted that I cannot control them, nor should I waste my time and energy expecting them to change. I can only control myself, and how I react. I try focusing on the good things, if only because it makes me feel better. My dad was always a good provider, and my ex-wife is a terrific mom to our daughter. Turns out my job is a lot more enjoyable now that I'm not tired and hungover. And for all I know, the guy who cuts me off in traffic is racing to see a relative at the hospital. I realize now that my alcoholism and resentments fed off each other. Once I was away from the alcohol, I began to notice so many reasons to be grateful. I just couldn't see them before, because I was soaking my brain in depressants on a daily basis.
I do not in any way mean to make light of your pain. But from another angle, one might say, Wow, you and your mom had so many years together beyond what her doctors envisioned. She lived to see your son—to see you become a mom. That must have been a precious gift to her. And you defied the odds as well, adding a daughter to your family. Amazing. (My daughter was adopted, by the way, so I realize what a miracle your boy is too!)
Anyway, I'm rambling. I don't know if any of that helps. I am truly sorry for your loss. It's obvious she meant to the world to you, and that you two had a very special bond. I'm sure she would be very glad to see you reaching out for support.