The thing is, you are never going to recreate that ‘happy family’ dream you have in your mind. You are adults with fond memories of your mother. Your stepmother cannot pretend to be a parent to you and why should she, it would be weird. She has not raised you, or had an input in your early life. She may well be respecting that by not getting overly involved.
You perhaps had your father to yourself for a little too long, too used to him still spending a lot of his time with his children. But you are adults and if he wants to spend some time with someone who makes him feel and do different things then why not?
My fathers partner is the complete opposite to my mother, she has changed my father, and he says and does things he has never done before. They have a relationship unhinded by young children so it is bound to be different to what I saw of my parents marriage when growing up.
I accept that she is different but unless she has been deliberately mean I think you need to let go, move on a little.
When my children have grown up I hope they will allow the opportunity to be a little self-indulgent and take some time for myself. They have only seen me as a parent and that a parent was perhaps a different person before children came along. People change and evolve throughout their lives, I am different to the person I was 20 years ago for sure.
I don’t know why your parents never married, maybe you should talk to your dad about it. Perhaps that will help clear things up, and ease your concerns. Do you think she is a gold digger?