A Secret Crush at Work

I’ve been in a long-term relationship for five years now, but recently I’ve developed this secret crush on a customer who visits the bar where I work. He’s handsome and charming, and whenever he’s there, my heart races and I can barely focus on anything else. Last night, we ended up talking longer than usual, and he leaned in close as if to kiss me, but pulled back at the last second. It was a moment of intense longing for something that could never happen between us. Am I betraying my partner by even thinking these things? Is it normal to still feel this way despite being in such a stable relationship?