I never said you couldn't love more than one people in your life. What I never got about LP is how they fell in love with other people and loved them WHILE they supposedly still were in love with each other. Don't you people say they have always been in love with each other throughout the entire series? That's what I thinks is impossible to happen. Once you truly love someone, you just don't fall in love with someone else.
And yes, people do have rebounds but I think it was crystal clear none of them were, especially Jake and Lindsey, who were people LP proposed to. You don't marry rebounds, you sleep with them. Which means you have no feelings for that person. But LP both had feelings for Jake, Lindsey, Julian and Brooke.