In some cases there is a sense that even infertile couples “might” conceive a child. However, in others - say, the woman has gone through menopause or, even more definitively, the woman has had her ovaries and/or uterus removed (for legitimate reasons), or the man has had his testicles removed (for legitimate reasons) - there is absolutely no chance at all of a child being conceived.
God could, I suppose, decide to work a miracle in such a case, but it seems to me God could just as easily cause a man to become pregnant. How are these (admittedly) extreme cases to be reconciled with Catholic teaching?
According to the Catechism, homosexual sex is wrong because it is closed to the transmission of life. It makes no mention of homosexual sex not being unitive. I don’t think there is any way to argue that it is not unitive, without excluding certain forms of sexual expression between married couples which is not immoral (provided it is followed by procreative intercourse). In other words, it is not solely vaginal intercourse which is unitive, though of course that is the sole procreative sexual expression.