Caught Between Duty and Desire

I’m a first-year law student in a committed relationship. My fiancé is everything I should be grateful for, loyal, kind, supportive, but lately, I’ve been feeling this gnawing void inside me that’s hard to explain. It started when I met this older professor during one of the lectures on contract law. He’s charismatic and knows his stuff, but there’s more to him than just intellect; he has a way about him that makes you feel like everything is possible. I’ll admit it sounds silly, but every time we’re in class together, I can’t help but notice how he moves around the room with such confidence. His gaze seems to lock onto mine at times, and there’s this undercurrent of something electric between us, like a tension that both attracts and repels me. Yesterday, after our class, I found myself cornered by him in an empty classroom for what was supposed to be just office hours. He started reviewing my notes with detailed scrutiny, as expected, but then he looked up at me and said something about how passionate and driven I am. It wasn’t the first time he’d complimented me on my work, but this time his words seemed different; they felt like a prelude to more. I left that room feeling conflicted. On one hand, there’s everything to lose with my fiancé if I pursue something so risky and unethical. Yet, when we’re at home together, all the fire I feel for him is now tainted by this other pull that only seems to burn brighter the longer it goes unacknowledged. This morning, I woke up knowing I need to find a way forward. It can’t go on like this; every time I think of my fiancé’s name or see his face next to mine in our engagement photos, I feel a pang of shame and doubt. How do you reconcile being loyal while still acknowledging your desires? Am I the asshole here?