Ultimately I feel very sorry for OP who was badly let down by her REAL parents and ended up as child, being a care taker for her mother's feelings.
She is still sadly locked into angry, sad, teen mode. OP is devastatingly, emotionally immature even though she is a 30 year old trying for a child of her own.
Her stilted thinking is fracturing her family further, pushing away a SM who by her owns words 'has always been kind to her' and siblings who she loves. And her father.
I would put money on the fact her own mother thinks what she is doing is totally justified.
To me a stranger on the internet she is crying out for therapy to help her process her relationship with her parents and her childhood.
In the meantime she's carrying on like a spiteful cow ( as spitefully as her own mother was to her re her relationship with her dad - and as thoughtless as her father was to her in his actions ) oblivious to how toxic her behaviour is now.
She appears surprised she's no longer invited to the home of her SM and Dad who she has taken shots at ( I'm reading massive understatement) and who has been really nasty to.
I doubt the SM really cares what the baby to be calls her but I'm sure she's devastated that her DSD has dismissed her 17 years relationship as "nothing". And in the OP's words "that's just a fact".
Sadly OP hurts and isolates herself the most of all the characters in this scenario.
. Actually I find it so hard to believe that the OP can write all she has and not get a glimmer of insight that her SM has been a positive in her life.
Is this is a reverse?