You're mourning not so much your mom but the mom you should've had and the family life and stability she should've provided and didn't. She dumped all of you, elder sister included, for her addiction instead of being the mom she should've been.
Madness string 111573
Every night, I am awoken by the isms of our relationship - the small quirks, the in-jokes, the made-up language we used, the tone of voice we would speak to each other in, the food we'd eat together, the things we'd do together, the songs we'd sing together, our touch, the warmth of her body against mine, the smell of her perfume, the way she'd say my name in a cute way when I'd done something cheeky... so many things that are littering my mind right now.