Unspoken Longing

I've been married for five years now, and we have a good life. But lately, I've noticed an unsettling change within me. When a particularly charming student from my literature class visits during office hours, there's a flutter in my chest that feels entirely inappropriate. It's not like I'm doing anything wrong; these are brief interactions about coursework. Yet, there's this...this longing for more. I don't know what 'more' even means here. Am I going through some kind of midlife crisis? Or is it just the allure of youth and energy in an otherwise settled life? Any advice on navigating this strange feeling without breaking any rules or hurting anyone?