This is where the UK system in comparison is vastly more fair, humane and civilised. Same-sex couples can come with their partners on the dependent visas with sworn affidavits and proof of relationship (shared utility bills, photographs, travels records, etc.). Same-sex couples are treated the same as male-female couples by the UK.
I'm convinced the US will get there, but it will be a slow, difficult and nasty process that will leave a wake of hardship with many couples.