A study recently completed shows that a large chunk of men would be forgiving of an unfaithful female partner if the affair was with another female.
The numbers are startlingly high: 50% of men wouldn’t have a problem with the unfaithfulness, compared to only the 22% that would stick with the chick if the person she was cheating with were male.
Research shows that part of the problem is that the male’s perception of two women getting it on is erotic, and envisioning themselves joining the party is like the double rainbow of sex fantasies. There's also the fact that a lesbian liaison doesn’t carry the threat of offspring.
Interestingly enough, women responded oppositely as 28% of them would stand by their man if he was a heterosexual cheater whereas only 21% would stay if their cheat were gay.