I think that you just haven’t met enough gay men in long lasting, monogamous and caring relationships who truly believe that God made them the way they are, but they do exist. You admit that friendships between gay men may contribute to flourishing, but why would a celibate relationships lead to more flourishing than one that includes sex unless the sex adds something destructive to the relationship? For those gay men who have had it pounded into their heads from their churches and from society that being gay is bad and that sex between men is wrong, disordered or defective, that might indeed be the case. In fact, the notion that they are in some way defective (this also applies to those who are struggling to remain celibate) is bound to lead to a form of self hatred or self contempt. But as Anglican Archbishop Desmond Tutu says in his book God Has a Dream: A Vision of Hope for Our Time (p. 54), “Not to forgive leads to bitterness and hatred, which, just like self-hatred and self-contempt, gnaw away at the vitals of one’s being. Whether hatred is projected out or projected in, it is always corrosive to the human spirit.”
For those gay men who have forgiven themselves for being gay and who do not think that they are defective or disordered and have truly come to accept and love themselves and truly believe that God loves them just the way they are, sex with their partners or spouses can, in my opinion, be just as positive as between heterosexual spouses. As Desmond Tutu says (pp. 47-48), “God just wants us to love each other. Many, however, say that some kinds of love are better than others, condemning the love of gays and lesbians. But whether a man loves a woman or another man, or a woman loves a man or another woman, to God it is all love, and God smiles whenever we recognize our need for one another.”