Why do human beings place such a great importance on companionship of the opposite sex?

It's a part of life for most people. If people didn't date, there would be no marriages and no babies being born. I agree that dating brings about those types of emotions that you listed, but life is full of emotions. That's just how it is. If dating isn't for you, then that's ok. You have that right, but that's not going to stop others from doing so.