Yes, I understand how sexual attraction works. In this case he didn’t shrink six inches, though, or shave his head or quit his job to join the circus or do anything else to change his “type.” He’s not asking you to fulfill some new kink or to alter the terms of your relationship. 

Same guy, same body, same personality, same relationship, except he could date a wider range of people than you thought if he weren’t already dating you and that somehow changes everything. It’s biphobia, OP. It just is. There’s no other way to describe the experience you keep describing over and over on this thread in the hope of being able to call it something else.