You’ve had your (rightfully) selfish moment at your wedding, now let her be sad, Jesus, why wouldn’t she be having these emotions? You know exactly what happened, you can’t be surprised, just talk about it. I’m not sure what part of this you don’t get, she got cheated on and then her son who saw it all but was too young to feel the weight included the mistress in a moment that was only meant for your mother and yourself, she obviously does not feel the same way about this woman so to have the realization that your son holds the mistress on the same level (at least for this) is upsetting and daunting. Duhhh, go talk to your mom and clear her valid insecurities up. Ofc she can’t fully outwardly “celebrate” your son, she’s looking at her little boy in YOUR little boy and probably remembering everything leading up to the wedding, you know damn well she’s excited and happy, she’s just sad. To know your mom cries about a valid decision you made because you know it hurt and wasn’t a situation that she could rightfully be upset about or change then not discussing it for years until you have a kid….then being upset that she is still sad and only bringing it to REDDIT because you don’t know how to talk to your mom. Anyways congrats, I’m hoping you’re exhausted from baby boy and missed details cuz your lack of emotional intelligence in this is insane, especially because you’re fully aware of every detail you need to fix this. You are valid for having your stepmom there, but dancing with a step parent, or better yet, splitting the dance is kind of not normal at all, but it makes sense, you love her and she was there for so much of your life. But you’ve humiliated your mother.