I’m married, and I’m sterile, have been since I was a kid. Does that make my marriage worth any less than yours?
God blessed man and woman with the words: "Be fruitful and multiply." Hence, true married love and the whole structure of family life which results are directed to disposing the spouses to cooperate with the love of the Creator.
As to your question, no, your marriage is not worth any less than mine. Spouses to whom God has not granted children due to sterility for instance can, as the Catechism teaches ...."nevertheless have a conjugal life full of meaning, in both human and Christian terms. Their marriage can radiate a fruitfulness of charity, of hospitality, and of sacrifice. (CCC, #1654).
Impotence is a barrier to Catholic marriage (Can. 1084 §1, states: "Antecedent and perpetual impotence to have intercourse, whether on the part of the man or the woman, whether absolute or relative, nullifies marriage by its very nature") but sterility is not (Canon Law 1084 §3 states "Sterility neither prohibits nor nullifies marriage, without prejudice to the prescript of Can. 1098.")
Why are you confusing issues of the will, homosexuality and contraception, with issues of the flesh, disability and incapacity?
That depends on whether you're married to a qualified individual, an adult of the opposite sex. In such a way, you model the ideal culture-enhancing combination which is marriage, sterile or not.
Homosexual relationships are not even "sterile" in the proper sense of the word - sterility implies at least the ability to reproduce were it not for some defect in a component or a deficiency which would otherwise allow for natural reproduction by design. Men and women were designed to reproduce together. And marriage bridles this purpose to society's benefit.