From the decision

It's 2-1.  THe opinion is narrow, applying specifically to the unusual situation in CA where a right was given and then taken away. This probably makes it a sturdier decision. From the opinion (my emphases)

….all parties agree that Proposition 8 had one effect only.  It stripped same sex couples of the ability they previously possessed to obtain from the State, or any other authorized party, an important right--the right to obtain and use the designation of 'marriage to describe their relationships.  Nothing more, nothing less.  Proposition 8 therefor could not have been enacted to advance California's interests in childbearing or  responsible procreation, for it had no effect on the rights of same sex couples to raise children oron the procreative practices of other couples.  Nor did Proposition 8 have any effect on religious freedom or on parents' rights ot control their education: it could not have been enacted to safeguard these liberties.

All that Proposition 8 accomplished was to take away from same sex couples the right to be granted marriage licenses and thus legally to use the designation of 'marriage' which symbolizes state legitimization and societal recognition of their committted relationships.  Proposition 8 serves no purpose, and has no effect, other than to lessen the status and human dignity of gays and lesbians in California, and to officially reclassify their relationships and families as inferior to those of opposite sex couples  The Constitution simply does not allow for "laws of this sort" (Romer v. Evans.)