For obvious political and social reasons, it's hard to be sure how many people are homosexual. Note that we are interested only in obligate homosexuality - bisexuals presumably don't have strongly reduced fitness. The Wikipedia article doesn't really distinguish obligate homosexuality from bi-, pan- and even trans-sexuals. The discussion in the SSC comments used an (unsourced?) range of 1%-3%, which seems at least consistent with other sources, so let's run with that.

Was obligate homosexuality common in the ancestral environment, anyway? If I understand correctly "gays" exist as a recognized social identity only in modern Western societies.
People engaging in homosexual intercourse and relationships probably always existed everywhere, and typically societies with significant influence of Abrahamic religions considered such behavior as a sin and/or a crime while non-Western or pre-Abrahamic Western societies tolerated or even encouraged it, but the general expectation was that people entered heterosexual marriage and had children.

Maybe there is a genetic predisposition to homosexuality but it is unlikely to result in obligate homosexuality, and therefore infertility, outside the specific environment of modern Western societies.