I thought I could trust my mom

Oh boy was I wrong. I told her a few months back that I'm gay, and she didn't believe me at first. I took a while for her to realize that I'm not joking. I asked her to keep quiet, as I want to find the right time to tell the rest of my family.Today, I had a little fight with her, and she made a big deal out of it once again (that's what she always does), so I just went to my room because I didn't want to deal with her anymore. Then my dad went to her and wanted to calm her down, but she started another fight with him. She was pretty loud, so I could hear their argument, when suddenly she says: "Did he tell you he's gay?"I couldn't believe what I just heard. And it took a while for me to realize what she just did. Not only did she out me to my dad, whose reation I was afraid of the most, she also completely destroyed all my trust I had in her with just one sentence. What's worse: judging by how casually my dad answered "No", he must've already known. When I realized this, I just couldn't crying. I'm typing this right now, still with tears in my eyes, and very afraid to confront her about that.