Ladies, I need to vent and be told that I’m just completely in the wrong. (So it’s long and I’m sorry I just don’t know who to turn to..)

My boyfriends sister, who I thought we were very close; back in March texted me saying their mother told her that I was telling the mom everything her daughter was doing. She’s 19. I told her no, because it was her business and I wouldn’t do that to her and that I was hurt she would think I would do that. Her response was I was an obsessive psycho bitch and blocked me from everything. I was really hurt and did not want to assume that their mother would do that. She said she never wanted to talk about it. It caused a lot of fighting between my boyfriend and I to the point I said i don’t want to come in between you and your family, that it wasn’t right and we were going to break up. But I didn’t want to lose him and said I will take your mom out to lunch or dinner to talk. And that was fine only his mom would always just say no. So of course I felt what his sister said was true, she was saying it was me when it was the mother all along. Hell months later we tried to go visit the sister and she said we could stay there but she wasn’t going to be there. Fast forward, now his sister and I are both pregnant at the same time. We are going to have a personal gender reveal then a huge baby shower where we will invite everyone, but the gender reveal I just wanted only people who actually supported us and cared. I made the exception for his mother but I told him I didn’t want his sister there, she could be at the baby shower. He didn’t care but the mother made a big deal about it. I said okay then let’s be freaking adults and talk about this. Said let’s meet and talk about this or over the phone. She ended up calling me, tells me I’m sorry you hurt your feelings but I feel like what I did was right at the time. I responded so just assuming and saying that stuff was right? Her mom then jumps in talking about how I just assumed that the sister was saying her. I said I have the text messages stating she said it was you( the mother) and when I tried to confront her about it just blew me off. After her mom was just going off. Stating family is going to fight. I responded okay I understand that but if we can’t be adults and sit down and actually talk so things aren’t assumed then I don’t know what to tell you. I’m not going to do this again because it’s taking a toll on my relationship so either tell me it’s not going to happen again or don’t bother. She responded why would it take a toll? Then told me I’m sorry but I don’t need this stress on my plate right now. I just boiled because here I am in and out of the hospital, fighting with my boyfriend, and worried about my child that was already a miracle that happened. I just said fine and hung up. Boyfriend says they won’t say anything but I’m like I don’t even want to be around people like this. I just want to cancel the whole thing, I want to cry, and just being told I need to just suck it up, swallow the pill, because I’m the only one who’s hurt and upset by it...