From what I hear...not hugely common but it happens. Also bisexuals may not sleep with "only" women but maybe more often - I don't have staistics. There's the Kinsey scale, 0-6. People who are "0" (complete straight) probably not, but there is a lot of grey area.

I've also heard that India is seeing the other way around. Ages 20-24 the ratio of boys to girls is 112.5 to 100. Young men-to-women ratios are much more skewed in Northern India. So....more young men are turning to each other for companionship, who ordinarily wouldn't.