I would be absolutely heartbroken. If my son did this to me I have a two year old child and well there are many supportive and wonderful stepparents. You only have one mother who carried you gave birth to you. Add morning sickness, went through the pain of delivery was up every two hours feeding you changing your diapers watching your milestones holding you when you were sick. Your stepmother didn’t do that. She has zero blood relation to you and while I understand you are close that is not your mother is your mother is heartbroken and devastated. I feel so bad for her but you have to do what you have to do if you really wanna dance with your father’s wife who you love that’s absolutely your choice but what a public humiliation for your mother, your showing everyone that she’s not special you have two mothers, and that would kill me if my son said that to me