I and my fiance have been together since our sophomore year of college, so around five years now. For context, my mom had an affair with a co-worker when I was 16, leading to my parents divorce. She has been single ever since. I have a good relationship with my dad and his new wife. Sadly, my fiance's mom passed two years ago due to cancer, and his dad has been single since. My fiance proposed last year, but our wedding was delayed due to COVID. Our families had never met up to this point because his family lives in South Carolina, whereas we are in North Carolina, about a three hour drive away from his dad. Three months ago, in January 2021, we decided it was time to have our families meet for the first time to discuss our upcoming wedding in June 2021. My dad and his wife, my fiance's dad, and my mom all met up at our place to discuss the wedding. This went well, albeit there was some tension between my mom and my dad. This morning, out of the blue, my mom called me and announced that she had eloped. I was shocked, as she had not been dating anyone to my knowledge. Upon questioning, it turns out that she and my fiance's dad have been dating in secret since that meeting in January and married in secret yesterday, making my fiance my quote unquote stepbrother. I want to throw up just thinking about this. She said that I should now cancel my wedding because it would be inappropriate to marry my quote unquote stepbrother. I am absolutely horrified. I shouted at my mom saying that she just loves to ruin my life, and I called her selfish. First she cheated on my dad, and now she went and married my fiance's dad. Knowing full well I was about to marry my fiance. My mom then said, I was still young and I had the chance to meet someone new, but she said she's old and she has to take every opportunity she's got, and I was such an ungrateful bitch for not approving of her marriage. She then accused me of wanting her to die alone. I don't think I'm the asshole, but I just wanted to make sure because ultimately I don't want her to be alone, even though I think she did that to herself by hurting my dad. I think I should be allowed to marry my fiance as we met first. I am also 12 years pregnant with my fiance's kid, so that complicates matters more. We haven't told anybody yet. Am I the asshole for being mad at my mom for marrying my fiance's dad, and because she said I can't marry my fiance anymore?