My Friend's Partner and Me: A Complicated Situation

I've been teaching high school for five years now. It's been my dream career since I was a kid. Over the past year, though, I've realized there's more to life than just education. My partner of eight years suggested we try an open relationship about six months ago. At first, it felt like a breath of fresh air, both of us exploring our own connections while maintaining our core relationship. But lately, things have gotten complicated. Recently, I started seeing someone new. He's a former student, now in his twenties and working full-time at an accounting firm. His name is Alex, and we connected through mutual friends, never once mentioning my past career or the fact that he used to be one of my students. We've been talking for months, but it wasn't until this weekend that things escalated. We went out for drinks with some other friends and had a few too many cocktails. The conversation turned to old memories, and somehow we ended up reminiscing about high school. At one point, Alex shared an anecdote from his sophomore year when he thought I was particularly strict on him regarding a missing homework assignment. In the moment, it struck me as odd how fondly he remembered it, or perhaps how much more positively than usual, given that Alex usually isn't prone to excessive nostalgia about past teachers. It wasn't until late into the night when we were alone at his place did I realize the full extent of our shared history. We sat on his couch in a comfortable silence for what felt like hours. There was no need for words; we both knew there was something lingering between us, some unspoken tension that had built up over years. I tried to maintain professional boundaries when he reached out after graduation. I avoided seeing him as much as possible because it complicated things, but now, in this moment of truth, I found myself giving into the attraction that had been simmering for too long. We both agreed that what we were doing wasn't exactly fair, especially since Alex was still in a relationship with someone else when he first reached out to me. Yet here we are. Now I'm stuck in this awkward position, wondering if it's really worth the risk. Should I have waited until his situation changed? Am I crossing too many lines by seeing him now that he’s an adult but still bearing a history from our past? It feels like every decision comes with its own set of ethical dilemmas and emotional turmoil. I guess what I'm truly grappling with is how far the impact of my actions can reach, especially when it involves students-turned-people-I-know-personally. It's hard to reconcile those lines in a world where past meets present so seamlessly.