Now that others have shown you just how ridiculous it is to only define love within a romantic and sexual relationship as you say - we can move on from those stone age notions since we know your opinions on what love is holds no factual truths.
So let's once again answer for you why a homosexual is sexually attracted to the same sex and not the opposite and why a heterosexual is attracted to the opposite sex, but not the same sex.
When a gay man looks at another man he may be attracted to his face, voice, eyes, lips, hands, arms, chest, build, frame, behind, skin tone, his haircut, hair color, his confidence, personality, his style, and later potentially his private parts.
When a straight man looks at a woman he may be attracted to her face, voice, eyes, lips, breasts, legs, frame, hair style, hair color, behind, skin tone, her confidence, her personality, her style, and later potentially her private parts.
Now obviously this is just a rough picture of what a heterosexual and homosexual man finds attractive but it answers what these two orientations are looking for. A gay man looks for masculine features while a straight man looks for feminine features. Why you ask? Because we're all wired differently.
But what we do know is what starts as a sexual attraction can later develop into a romantic loving relationship for both sides, depending on what kind of chemistry you both have and if you both click. Your personal definition on what love is doesn't refute that.