This, right here! I feel this in my guts! I was adopted, like, they actually made a conscious choice, and my mother hated my damn guts! I grew up as "the other," the one that wasn't "Brucie," the one that was never wanted (yes, she said it).
Funny thing, when she was old and helpless and I became a lawyer, she LOVED me! She had something to lord over people's heads. She had something to set her apart.
Is it possible your mother doesn't deserve you? Fuck yes! Is it possible you deserved better? Absolutely. Sadly, there's no handbook or rule regarding who can spawn young. Her inadequacies as a mother have nothing to do with your worth as a person....Hear me, really hear me....SHE wasn't equipped, SHE had the issue, you were just born. You were innocent and perfect as you were.
I get it's a head fuck, both my husband and I deal with it every day, I mean who else is supposed to love you without reservation, right? You know who? You! She didn't have it to give. You do. Because sometimes all we can do is give that love we wish we had to ourselves. I know it's hard, believe me, I know.