no. no relationship should be considered marriage, because some people don’t want to be married. man and woman relationships are not considered marriage, either. you have to go to some authority to get married, and yes, same-sex couples should be allowed to do so.
I actually think that we should do away with marriage as a legal construct. Leave marriage for the religious, and allow anyone who wants to to enter into legally binding contracts that provide for all of the things that “marriage” currently does. Grandfather in all of the people who are currently married. People who want to get married in a religious ceremony may, but they will also need to gill out the paperwork to give their marriage any legal meaning.
We already have a long and detailed thread on this subject (two of them, actually). Please visit that one and add on to it if you would like to comment on gay marriage. I have no problem with it being brought up again, I just want to limit the number of threads about the same topic.