It will all come down to can you vote on what rights others are allowed to have
It will come down to "does the State have a compelling interest in legislating the activities of people in the bedroom" and the answer is yes. Unless you think Polygamy and Incest between consenting adults is ok.
But this issue is not even about sex it is about the ability of the abnormal to marry. And the decision will also hinge on the concept of " what defines marriage". And do the States have a compelling interest in regulating the institution of Marriage. The simple answer is YES the State DOES have a compelling interest. The follow on question being does the State have a compelling interest to define what is and is not marriage. And again the answer is yes they do.
The final decision will be nearly unanimous though, due to the political climate and the cowardice of many the Supreme Court will most likely vote 7-2 or 9-0 to agree with the 9th.