This is one of the biggest reasons I am not in a relationship. This is what I am. I am totally 100% loyal, committed, and interested in only ONE woman.
So what's the problem you may ask? The PROBLEM is that I expect the same from my lady. When SHE expects, wants, and receives 100% loyalty, it's because she "loves" me.
But if I expect the same as what I offer and give, I am possessive, insecure, a narcissist, and a control freak. So I choose to do without the BS. The arguing, the hypocrisy, and the double standards. We live in an extremely self centered society. A relationship which you describe takes TWO, and two unselfish people getting together these days is rare...or yes, unrealistic.
And a sure fire eventual death to most relationships is "girls night out" or "guys night out". Nothing good can come of it.