By your reasoning, any cohabiting couple could be accused of 'grave sin'.  How does one know a married gay couple is embracing a gravely sinful homosexual lifestyle?  What if they are actually celibate?  What if someone wrote this about their same gender housemate of 32 years:  ""I have always thought no bereavement was equal to that of a husband's or a wife's," he wrote, "but I feel it difficult to believe that anyone's sorrow can be greater than mine."  Would you say this person lived a gravely sinful homosexual lifestyle?  Those words were written about Ambrose St John by Blessed Cardinal John Henry Newman.