Because the notion of sex is implicit in some sexual orientations. If you fire a man for loving some individual, but not fire a woman for loving the same indiv

Because the notion of sex is implicit in some sexual orientations. If you fire a man for loving some individual, but not fire a woman for loving the same individual, then that is discrimination on the basis of sex. The question that I think is still untested is what happens when you consider someone asexual or bisexual, as that isn't as simple a case to handle as just flipping the genders. If you fire a man for loving two people and fire a woman for loving those same two people, it doesn't appear you are discriminating based on sex. But given that such a relationship would also be considered poly-amorous bisexual and not monogamous bisexual, and given that the likelihood of having a business that only fired people for poly-amorous bisexual relationships and not for monogamous homosexual relationships is extremely small, I'm guessing it will be some time before it is tested in courts.