I admit your post was kind of hard to follow, but I think I got the gist of it.
Let's consider sickle cell anemia as our subject for emphasis, instead of homosexuality, and then look at it's implications. We'll use H and h as our alleles for sickle cell anemia, similar to how you used H and h with homosexuality. So with that said, let's begin,
If H gene (for Sickle Cell Anemia) is received from both parents, the subject will be afflicted. (HH)
If h gene is received from both parents, the subject will not. (hh)
Now it gets interesting. If H gene is received from one parent, and h from the other parent (Hh) a strange trait develops. Hh becomes resistant to malaria. Look it up if you don't believe me. This is one of the few examples of a
heterzygous advantage in humans. This opens up the theory that homosexuality may actually be beneficial to us.
So why would a bad gene have have a positive counterpart trait, like resistance to malaria? The answer is not simple, but perhaps it is related to how homosexuality works. Also, I feel like it's worth mentioning that natural selection typically works on
population as opposed to
individual. These are all triggers based on the subject's relative closeness to the said gene (h) within its' own population, ie kin (and there are many, many biological factors as to what trigger the genes/trait - but in utero hormone levels are key in the the case of homosexuality).
So again, one way to look at homosexuality is that it offers a heterzygous advantage in the subject, i.e. it is a combination of the kin's trigger genes that results in a positive outcome in the subject ie homosexuality. Why? Because evolution works on the scale of large population as opposed to individuals and because we are very, very complex creatures - especially when it comes to genes and the brain.
TL;DR genes are not fully responsible for triggering the homosexual trait. It's a slew of different conditions, but genes and biological factors are the biggest factors. IF there is gene for homosexuality, then it's tied up with all those additional biological factors which we silly humans are still trying to decode. It's science!