What we humans call... Love?

How can two people with two totally different life plans become so intertwined with each other. So in love with one another that they would do anything for, yet can't seem to match lifestyles. How can they be so in love that while one sleeps the other is most awake, and while the other is making compensations the the other seems to striving for what they've always wanted? How can they be as perfect as they believe when they argue anytime one does something the other disagrees with. Should one of these people forfeit their desires and dreams to see the happiness of the other? If their love is as strong as they feel would this be a reasonable and logical thing for one of them to do? When you fall in love and decide to become one with another do you eternally deprive yourself of what you feel you'd be most internally satisfied with? Or do you combine your dreams with your lover and make sacrifices while they do the same? Obviously there isn't a manual on life or love, but if there was would the answers to these questions be in it?