I don't know that he had much choice - he was seen in a gay bar, left with another man, and caught in the DUI. After that hit the news, others started coming forward saying that he was frequently at gay bars. Makes sense for a politician to admit something that's going to come out (in both senses) anyway. Not that I think it's going to help him, or should help him, but it's his best chance for political survival.
Political survival is impossible now. In an election year he cut his own throat.