If a gay judge needs to recuse him or herself from a case that involves gay marriage, than heterosexual judges would need to recuse themselves from cases involving heterosexual marriage.
But, of course that does not make sense.

The sexuality of a judge should not have any effect on their ability to judge cases.
If a heterosexual judge can be presumed to be able to judge a case involving heterosexuals, why would not a homosexual judge be presumed to be able to judge a case involving homosexuals?