This shows a profound misunderstanding of evolution and natural selection on your part. "Evolutionary benefit" is impossible to divorce from circumstances. It doesn't exist as some right/wrong answer, or something you can divine through logic.

For instance, same-sex attraction could absolutely be advantageous to a species that is nearing the peak of sustainable population numbers. All species (who can fuck) wanna fuck, and will do so no matter their surrounding circumstances. The difference between one species keeping sustainable numbers, versus another species seeing runaway population numbers causing food source exhaustion and population collapse, could come down to lower procreation rates, in which circumstance strict heterosexuality may not be advantageous.

Point being, stop trying to use bad, dime-store "science" to justify your bad opinions about homosexuality.