There is a range of ways men can array themselves with one another, but most of the traditional forms of relationship depend more or less absolutely on the concept of ownership. The two people in the relationship own each other. They can’t have sex with anyone outside the relationship, they can’t spend time with someone outside the relationship. These forms of coupling come at a high cost, as men wander, and as both sides in the relationship levy charges of betrayal. 
Some gay male couples avoid this pattern by specifically not claiming ownership. A man is free to go and come as he wants without being questioned by his partner. No one in such a relationship is ever asked, “Why didn’t you come home last night?” Or, “Where were you last night?” Each man in the relationship is absolutely free to do exactly what he wants to do whenever he wants to do it and does not ever expect to be questioned on it.
In such a relationship, both men avoid making promises—specifically the promises in the traditional marriage service about monogamy and about staying together till death. The assumption is that these couples will stay together as long as it is good for both of them. These relationships are often opened up to include a third partner or a number of other partners who stay temporarily. 
There are, of course, other ways for men to come together. Books have been written on the subject. My point here is that many of us know men whose relationships would have to be described in a whole range of ways. What is notable about the gay community is that, in the centuries during which we have been excluded from heterosexual marriage, we have used our time well. We’ve explored what was possible, determined to find out what worked and what didn’t. Many of us have concluded that ownership of one’s partner doesn’t work, and all that emotional energy expended on expressions of betrayal and grief because the other person has acted the way many men act is merely wasted energy. We have learned that sex is not the same thing as love and that the quickest way to destroy a relationship is to act as if everything were to depend on sexual fidelity.
Now then, at this point, when we are about to start marrying legally in ever-increasing numbers, it would be a shame if any large numbers of us forgot the rich history of gay people, forgot the ways we learned to act when legal marriage was closed to us, forgot that we learned years ago that feelings of betrayal are really just wasted energy, and forgot that we know more about what men are sexually than anyone else in our culture. If we start arranging our relationships as if we were straight people, presided over by a priest, we will have betrayed ourselves and we will have betrayed the great history of gay people.