That cannot possibly be true.
Wikipedia says 2-5%
There is absolutely no clear and obvious difference between heterosexual and homosexual relationships.
One is an expression of the naturally evolved sexual behaviour of the human species (and all sexually reproducing mammals) and the other is not. Sex evolved with a function. To reproduce. In order for it to work it has to be between members of the opposite sex.
The lungs evolved with a function: To keep us afloat in the sea when we were still fish. Using them for breathing is obscene. Our limbs evolved with a function, to paddle. They were never meant to be used for stalking. In order for them to work, you have to be immersed in water. So what are you still doing on the dry?
The amniotic sac evolved with a function: to prevent the egg from drying out, thus allowing us to lay our eggs on land. How dare those fucking mammals (and some viviparous reptiles) not use it properly?
The larynx evolved with a function: To prevent food and water from getting into the (already misused) lungs. It was never meant for producing sounds, so you better shut up for the rest of your life.
The opposable thumb evolved with a function: To better climb in trees. So stop using your hands for typing.
The answer is, evolution doesn't work that way. The origin of an organ or instinct is an interesting question in its own right, but it is insufficient and often misleading when your goal is to find out about its current function or function(s). An organ that evolved for one function can turn out to be useful for other purposes too, and henceforth its evolution will depend on the requirements of more than one function. Organs, or instincts, don't have one eternal and inherent purpose, and everything else is a misuse. In fact, labelling something as a misuse doesn't even make sense from an evolutionary perspective - either it works, or it doesn't. Sometimes those chronologically secondary functions can entirely replace the original function which becomes obsolete (such as the lung as a floating aid), sometimes they co-exist peacefully, and sometimes they co-exist in a tug-of-war, with the different functions imposing different and opposing requirements on the same organ leading to a fragile equilibrium, with possible complications both ways and the possibility of a fairly rapid transformation if one of the functions suddenly becomes more important (this may be the case for the human larynx - it's lowered position, improving our vocal capacity, is actually the deep cause of quite a number of choking deaths especially among infants every year).
So, yeah, sex did evolve for reproduction, but reproduction isn't and hasn't been the only thing humans and their ancestors use sex for, since long before homo sapiens even existed.