Is Anyone Truly "Straight"?

Is anyone truly, exclusively attracted to one gender or have those who think they are just not met the right alternatively-gendered people? Example: I'm almost exclusively, strongly attracted to men but the right person will have me crushing, sometimes even head over heels, regardless of what's downstairs or how they identity. (My ex gf Crystal, L-Word's Shane, my friend Hope, my mother-in-law's friend Debbs, my school friend June, and others are are prime examples.) I understand that certain things are just deal breakers for various people but the heart and body want what they want and can you honestly say yours would never want anything beyond what you're used to? I respect it if so but I just can't imagine that feeling.