My (16M) parents divorced 5 years ago, and my dad met my stepmother a year later, and married her last year. I was very upfront with her that my mom is still alive, and I won't ever consider her my mother figure or a family member. She's my dad's wife and that's all she'll ever be to me. I don't tell her I love her, because I don't, when she calls me her son I correct her.
Mothers day is in two months, and I mentioned to my dad while I was over to the weekend that I was just gonna go get something while I'm over at his place, so she doesn't know. His wife (I don't call her my stepmom outside of context reasons) started suggesting ideas for what I could get her. I asked why I'd get her anything. She tells me because it's mother day.
Here's where I might've messed up. I told her "I'm not your son and I'll never be, you're just my dads wife, and I'm not getting you anything. Stop acting like I'm you're kid" She started crying and my dad lost his shit, and called my mom to pick me up. He told me not to come back unless I apologized, but I don't think I did anything wrong besides be too harsh. But I'm sick of her acting like I want to be all lovey dovey with her.