Are you more likely to forgive if your partner confessed sleeping with a person of same sex behind your back? Let's be honest!

Of course not. Cheating is cheating, whatever the gender. In fact, I would probably be more pissed off that he found someone of his own gender more attractive than me! The baseline is, I'd feel hurt regardless of whether the 3rd party was male or female. It's the betrayal of trust that kills the relationship.