I need to Vent!

Ok so me and my SO was spending time with his daughter and her grandma today. We'll when we left I told my SO that really does bug me that he calls her mom because he is not with her daughter and she is not his mom. And he said we'll it's just easier and I never had mom growing up. We'll he didn't took how I said it like he didn't care. And I get we are 2 different ppl but I ask him also please stop calling my mom . Mom call her by her name and he was like really yes I feel like if your going to call someone else mom. No reason to do it to everyone. It bugs me really bad and normal that kinda stuff wouldn't bug me but it does. I wasn't raised like that and I know for damn sure he wasn't. But just cause he didn't have his real mom. He had his step mom and he don't call her mom! I just needed to vent I told him how I felt and he didn't seem to care.