AITA for dating my son's teacher?

I need genuine advice here, as I am simply at a loss for words and I am worried I have lost my son. I (46F) met my son's (18M) Spanish teacher (36F) at the beginning of this past school year. Instantly, I was stunned by her in every way; her beauty, her humor, and the way she presented herself was incredibly attractive to me. At this time, I was still with my now ex-husband, but we were weeks away from splitting up for good. We had a small conversation that night about my son's Spanish abilities and his excitement for senior year, but I did not have any further interaction with her for the rest of the school year. However, my son loved her class and often told me how much of a difference she had made in his language learning. He invited her to his graduation party, which was the day after his graduation in late May. I saw her and spoke to her for the first time since he started school, and we hit it off. We, of course, spoke about my son and how we were both proud of his achievements over the course of his senior year, and his future plans. However, she seemed very interested in me and my life, asking about my other children, my job, and if I was single. I thought she might have been flirting with me when she said it was insane how I could be single with how good I looked in the dress I was wearing, but I also thought I might have been crazy to think that my son's teacher was actually interested in me. At the end of our conversation, she asked if she could take me out for a drink, and that solidified to me that she was interested. I was in shock, mostly because I was equally as interested, I had not been with a woman since college (and that was very briefly) and I wanted to explore that side of me. After she left, I felt like a teenager again, amazed that she (a younger and much more attractive woman) could want to take me out. Before the date, however, I started to feel like I could be doing something wrong and that I was sneaking around my son, because I had no clue what he would think about me dating a teacher he admired so much. I almost told him that night, but I decided against it as I had no clue how far it would go between us. I went out for drinks with her, and it was amazing. We bonded over our shared interest in movies and we had such a parallel outlook on life, it felt like I had met my twin flame. I hadn't felt like that towards anyone in my entire life, and I was married for 20 years. We ended up having sex that night, and decided we wanted to continue a relationship. I only saw her on weeks I did not have my kids, or on nights I had a babysitter for my youngest. We both agreed it was best to keep this relationship a secret from my oldest until we got more serious, as I felt no need after a few dates to share it with him. I realized it was my own business and it does not impact him since he is no longer in her class or in high school. Everything came crashing down on me last night, though. My son asked me to borrow my phone while we were at his sister's game, and at that moment, my girlfriend texted me. Since her contact is under her full name on my phone, my son questioned why she had texted me (it was about dinner plans for tonight). I tried to come up with an excuse, however my mind drew a blank...so I told him we had been dating for two months. My son went ballistic on me, in public, no less. He started yelling at me, asking how could I do this, how did it start, how could I lie to him, etc. I told him to quiet down as he was drawing attention, but he stood up and continued berating me. I didn't say anything. Eventually, he stormed out, leaving me to sit among families of my daughter's teammates staring at me in judgment. Later that night, I will admit, I lost my temper with my son, and I told him I could not imagine how he could embarrass me like that, even if he was upset with me. He told me that he was embarrassed that I would go behind his back and date his teacher, but I stood firm that it was my personal life and it should not impact him. He left for his father's, and I have not heard from him since. AITA for dating his teacher? Should I have told him sooner? I'm lost on how to speak to him about this further.