Love VS. In Love

So I was thinking about this today at work. I believe that when two people are in love they get married and spend a life time of happiness together. Some people believe that when two people are together for 3 or 4 years that they should just get married because that's it. Now God bless the people who have choice a., but for those of us who get choice b...let's talk. I just am wondering that if you marry someone because you have been with them for so and just figure that, that's it your supposed to get married. What happens if you meet the true love of your life after that? Do you get divorced? Do you do nothing? How does that work. I know a man who is married and has a little girl but he is in love with someone else. That can't feel good. It;s not like he fell out of love with his wife he truly does love her, but he is IN LOVE with someone else. That's not fair to him, to know that this other woman is truly meant for him and will give him all the happiness in the world. It's not fair to his wife because she thinks all is fine and dandy. What happens then huh?