Well, there isn't realy a point to it. Initially, lifetime monogamy was about ensuring the transfer of land and assets from a man to his sons; women were the machinery used to make this happen. Up until fairly recently (in historical terms, eg a century or two) life was pretty hard for just about everyone, even the wealthier ones, so few people had that much time to ponder their emotional needs. And they died younger, too...
Post-industrial revolution, the point of monogamous relationships was that each man could work long hours for an employer, outside the home, and own a woman to take care of the childrearing and domestic work.
It's the perceived need for every man to own a woman as breeding stock and domestic servant that's behind all the present-day guff about the importance of longterm heteromonogamy: the fact that some people find it enjoyable is really neither here nor there in sociological terms.
So the bottom line is: if you like longterm heteromonogamy and have found someone happy to engage in it with you, good luck and fill your boots. However, if you have other priorities and/or you've tried it and it doesn't work for you, remember it's not compulsory and nor is it the 'best' way to live.