That was before his love affair with Obama the Sodomite. Watch Christie change his stance on this issue, just like Schwarzenegger.
Christie is for de facto same-sex "marriage" in the form of civil unions. He has stated, in very threatening terms after he vetoed the marriage bill, that he would come down hard on anyone NOT treating same-sex couples as married.
There is no substantive difference between these legally binding, legally obligative, laws and real marriage. Civil unions used to imply some of the legal rights of married people; for the past several years it has by default meant ALL the legal rights and incidences of real marriage.
So, Christie is actually in favor of fake "marriage."
Even if the intentions that you ascribe to Christie are 100% correct, he would still be unacceptable to Democrat primary voters, because he has opposed establishing same-sex marriage.