A troubling relationship situation.

I have been in a serious relationship for 2 years now, and we have talked extensively about marriage. Recently, however, I have reluctantly had to admit that I have it bad for someone I work with. He’s 10 years older than me, currently married (they separate at least every other day), and has three children. But he acts interested also. I never would have entertained this, and I am horrified that the thought has entered my mind. I cannot, however, deny these feelings any longer. Could this be infatuation? Or has it been that long since I have had an honest-to-goodness crush ala junior high?