Fr. Tobias Haller BSG responds in a post to the argument made by some who oppose same-sex marriages (or unions of any kind) when they ask a question such as, “Why shouldn’t three or more people be allowed to marry if they love each other?”
A paragraph:

A polyamorous or polygamous grouping of people may claim to (and perhaps actually) share a loving relationship among themselves. But “among” makes all the difference — it is not the same as between. Such a group or assembly may love one another, but they cannot love “each other” — that kind of reciprocal experience is limited to couples. A multiply partnered relationship cannot be “mutual” but must be “distributive.”

Read the whole post, Love Between, not Among.