Homosexuality isn't a choice and everyone is gay to varying degrees. I'm sure you've heard of heterosexuality, bisexuality and homosexuality, and the most common way to picture them is as three separate categories you can fit into. This however has been overwhelmingly shown not to be the case. The way it actually works is more a two dimensional graph, with attraction to women on one axis and attraction to men on the other. Let's make a convenient scale for reference: full attraction to a sex is to be considered a one, no attraction is to be a zero. Our graph would look something like this. So, at (x,y) -> (0,0) we have asexuality, at (x,y) -> (0,1) we have full attraction to women (heterosexual men, homosexual women) at (x,y) -> (1,0) we have full attraction to men (homosexual men, heterosexual women) and at (x,y) -> (1,1) we have full bisexuality. In a classical model, this is a discrete system, so you only ever see whole numbers. However, modern research into sexuality shows us that it's actually a continuous system. So, you could be a (0.6,1) or a (0.52,0.56) or a (0.975,0.343), that is you are attracted to both sexes, but unequally. That's why you'll sometimes here bisexuals say, "I prefer men/women". What's really interesting is that according to this current system, most people are not at the old markers. That is, most people experience degrees of attraction to both sexes, and societal pressure is what gets us to identify as exclusively one thing or another.

Now, most people are still almost exclusively heterosexual, so would have very high attraction to the opposite sex and very low to their own (but not necessarily zero). That brings up the question then: if I score at (1,0.1) would it be reasonable to expect me to sleep with women? I'd say the answer is clearly no, because this is around where most women who call themselves heterosexual probably fall, and asking a heterosexual women to exclusively sleep with women doesn't lead anywhere good. However, this is probably also where most men identifying as homosexual fall, so is it reasonable to say they can just sleep with women if they want to? If the answer was no for women above, I think the answer ought to also be no here. If you experience low attraction to one sex or the other (or both) sleeping with that sex isn't a realistic choice.