1. My partner and I have been together for 12 years (congrats on 19).
2. We're registered Republicans (but vote Dem more often than not).
3. Ask him if he would have backed the three-fifths compromise on counting slaves in the census:
http://en.wikipedia.org/wiki/Three_fifths_compromise4. At one time in our nation's history, supporting this Constitutional principle would have been considered "conservative," but now it would be considered "reactionary," and "the wrong side of history."
5. Tell him that you don't consider your relationship to be three-fifths of one, and that your partner and you should be entitled to all the protections of marriage that - say - a middle-aged couple who have no intent of having children should enjoy.
6. Finally, confront him with all of the "special rights" that he's fighting to exclude your partner and you from, while his side of the "marriage apartheid" line enjoy these:
http://www.thetaskforce.org/theissues/issue.cfm?issueID=14 (see the list of 1,138 ways that the GAO says that the Federal Government alone gives special rights to married couples; this doesn't even include the special rights granted by the respective states)
7. If you're going to argue with a "reactionary" posing as a "conservative," you gotta learn to think like one! The Constitution once defined slaves as three-fifths of a person: at the time, supporters even used the Bible, which mentions slavery as commonplace and normal, as support for the argument that slavery was ordained, natural, and lawful. Tell him that he's following right in the footsteps of those arguments, and invite him to explain to you how your partner and you should be taxed like anyone else, without sharing the same rights. Invite him to support the modern "Three-Fifths Compromise" that is "straights-only" marriage, and ask him if he'd patronize an establishment that had "straights only" and "gays only" counters, water fountains, etc. Gotta hit a "reactionary" posing as a "conservative" where it hurts: with examples of other poor, misguided reactionaries who thought they were being conservative, but ended up just being on the wrong side of history.
8. Finally, if that's not enough, tell him that if his ilk doesn't figure this out, the demographic voting wave that is Gen Y is going to put them out of power for a good long time:
http://www.google.com/search?hl=en&lr=&q=generation+y+voters; )
Hope that helps!
- Dave