do I have the right to be upset?

My stepmom, and I have had very serious issues for the past 2 or 3 years now. I’m almost 20 now, and I split my time still between my dads house and my moms house. I was over at my dads yesterday, and we were having a nice conversation. I will say, and I am not saying out of spite that she is DEFINITELY an alcoholic, and she tends to be either super nice or super unkind, and it’s really a gamble based on if anyone has said anything to set her off. Her and my dad have not told us kids until the night before multiple times that my dad is having surgery. My dad says they’re minor surgeries, and he just doesn’t want me to worry. She says she doesn’t want us telling my mom he’s having surgery or tell her side of the family because it’s only their business, and she will tell us the night before only. I told her that if she feels so strongly about it, then I won’t tell my mom even though I’m very close with her if it means I can stay in the loop. She got a little angry, so I dropped the subject because I wasn’t in the mood to fight. It does make me upset because I love my dad, and we were really close until her and I started having issues, but when he would side with me on occasions I was not in the wrong, she would threaten divorce on occasion, so he has kinda stopped meddling with our issues. I’m in no way trying to insinuate that I haven’t caused issues, but I already feel sad I’m not as close with my dad because of the past issues with my stepmom, and her excluding me from his health out of spite of me “ telling my mom” is even more frustrating. I’d like any any and advice anyone may have on this situation.