I read a great article on sex and gender as ingredients for marriage: http://www.boxturtlebulletin.com/2008/03/25/1692
Included is some ways, historically, that trans people marry. One of the points is that marriage has traditionally relied on having different genders, not different sexes. Since my gender is different than everyone I've met, this feels like good news to me! As well as the note some marriages don't involve any sexual activity.