Perhaps we need to invent new words like heteronuptial or homonuptial to describe these radically different realities. Using the same word to describe the two relationships is papering over the cracks of too many fundamental differences; the potential of a heterosexual relationships, the unity of heterosexual relationships, the complementarity of heterosexual relationships are all radically different from same sex relationships. They may be equal in value but they are radically different. Simply labelling them the same way does not remove the diverse nature of the two relationships so much so that other language will have to be created to make that distinction with much confusion as a result.
As a Christian I have little problem with gay relationships and recognise the hierarchy of values in the catholic church especially which places love right at the pinnacle of that hierarchy. St Augustine put it simply "love and do what you will." Many other Christians would disagree with this approach but I am not sure that Jesus would. His approach was one of compassion and encouragement to the woman at the well and the woman caught in adultery. The woman who was a sinner and wept at the feet of Jesus was not forgiven because of her moral strength but because "she had loved much."
Same sex couples cannot simply throw a switch and disconnect from the genuine love that holds them together. That love is as much part of God's love as is heterosexual love. Otherwise why would a consistent 11% of the human race, made in God's own image, be born with this orientation? Christians cannot pick and choose to recognise one love and not another, bless one kind of love and evict the other from public life. As a catholic church we have a lot to learn about sexuality. We are male, celibate and caught up in a clerical culture for millennia. We need to be a church that listens in this area and say little, perhaps for a hundred years or more. Listening will make us humble, perhaps even wise in this area and the Gospel may emerge with a greater clarity than ever before when we recall the words "God is love"
But the word +marriage- that is in for a difficult time +dictionary writers will already be scratching their heads and creative types will be dreaming up new, and hopefully better, words for heterosexual contracts.