Was I in the wrong? Baby mama and boyfriend problems.

I am pregnant with twins. My boyfriend has 3 kids with his baby mama and then expecting two with me. My mother and I are where having a girls day and we ran into my boyfriend, his kids, and baby mama. I tried telling my mother that maybe we should go somewhere else… we went to a clothing store to find Easter outfits. Well, my boyfriend noticed me and walked up to me and gave me a hug and said hello and to my mother. His baby mama got mad. I just walked away and minded my own business. I don’t understand why she has a problem with me but she does… well while looking at clothes.. he came and said that he just wanted to tell me bye and kissed me. She got mad at him again and said that was rude of him to come talk to me while he is hanging with her and the kids. I don’t understand what I’m doing wrong. I’ve tried to be nice and civilize and I’m trying to see her POV in all of this. The reason they are not together is because they were so toxic for one another… am I in the wrong?