How do I (28M) tell my dad’s wife (57F) that she won’t be mother of the groom at my wedding and we won’t be dancing together?

I’m in a sticky situation here and I want to be compassionate to a point without making this something that gives this woman false hope. But our background is long and it’s proving difficult for me to not just be blunt about this.

My mom died when my brother, sister and I were kids. My brother was nine, sister was seven and I was four. Two years later our dad brought home his second wife, though she was only a girlfriend at the time. She was super excited to meet us and I remember her being very affectionate to the point it made us uncomfortable. Like hugging and kissing on us and trying to hold our hands. My sister told dad and that stuff stopped but she was still really excited to be coming into our lives. So my dad married her.

After the wedding his wife had a hard time settling into things. None of us called her mom like she wanted, there were photos of our mom around the house and we had mom’s last name instead of her and dad’s last name because our mom never changed hers when she got married to dad. And we got her name when we were born.

The photos in the main part of the house came down and then she tried to remove them from our bedrooms and the playroom which only had one. She insisted to be respectful of her we needed to not have any up anywhere and to keep them in boxes until we moved out. It turned into a fight where dad told her she needed to stop before she broke the photos and just accept that we could have them in our rooms. My brother and sister shut her out completely after the photos though and she turned most of her focus to me, her “baby boy”.

She tried so hard to mother me and to win my love. She asked me the weirdest questions like why I loved my mom. Or why I enjoyed spending time with my grandparents. Why did I never ask her to do things with me. And she even asked why I let my siblings decide who my mom was. Those were typically followed up with her saying she was the only mom I’d remember after a while and suggesting I could steal the photos of mom from my siblings room and give them to her to take care of. I didn’t entertain this ever but it made me really mad at her. I was just bad at expressing that at the time and I’m the quietest of my siblings so I never made the big fuss they would. So she always had this hope for me to become hers.

She also broke our mom’s coffee mug “accidentally” but we all had our doubts that it was an accident. Even dad suspected she did it because she was jealous.

My siblings were pretty ruthless in how they treated her and I supported them in doing so and even cheered them on but she was blind to that and my quietness she took as love for her. She had dad ask me if I wanted to be adopted and change my last name a couple of years after they got married. I said no and he accepted that but she brought it up to me a lot.

I was twelve when things boiled over. Our maternal grandparents wanted to take us on vacation and we wanted to go so the five of us talked to dad. His wife took it as I was being pressured into going by my grandparents and my siblings and she had a breakdown where she told them they couldn’t take her son and to stop getting in the way of our relationship. She told my grandparents that I hardly remembered their daughter and she was the only mom I would ever really remember and they needed to accept that and back off.

Her and dad ended up in therapy and she went through individual therapy. Dad sat the three of us down after that and told us that she was going through a lot of deep insecurity and it’s why she was acting out like she was and clingy like she was. He said she would work on that and could we please try to be understanding and not shut her out or be so awful to her. He asked me to just be polite. But even after therapy and she wasn’t as bad, she still had this belief that I was hers and that I loved her and that she was the only mom I ever really knew. I had few memories of my real mom but she was still the only mom in my heart.

My siblings and I all pulled away from dad over it because he stayed with her and we were done dealing with it. It took about 18 months of that before he came to us and asked us to go to therapy with him, which we did. We talked stuff out and he told us he really loved his wife even with all her flaws but he could accept we would never see her as anything more than his wife, not even a stepmom. He told us she was back in therapy too and she was working on backing off.

Things are civil but distant between me and her now. But my relationship with dad is closer than it was for a lot of years.

I got engaged a couple of months ago and about a week after my sister told me that dad’s wife was expecting to be mother of the groom and dancing with me when my fiancée dances with her dad. She said since neither her nor my brother really acknowledged her at all and because I was the youngest and she had her hopes on me for so long, it seemed like she still believed she was a mom in some way to me. I thanked my sister for telling me and decided to wait until dad’s wife brought it up and if she didn’t I wouldn’t say anything. I didn’t want to create problems. But now she has brought it up indirectly by tagging me in mother/son wedding dances and at a birthday dinner for a family member she talked about looking forward to her “role” in the wedding.

So now I don’t know how to bring this up with her. I was not planning on doing anything different to my siblings. But I can also see that I’m older that this does hurt her and she does love me, and even if don’t like or love her back she is a human and my dad loves her. So I need advice here because I’m at a loss. I can’t make a promise to give her something because it will only fuel this hope for more.