relationships

I have met many girls and guys who change boy friends like clothes so often. But have often wonderd what are the emotions they are going through. What is it that drives them through relatonships. What do they feel.... The yseem to be so dedicated to every relationship they are in, yet the transition form one to another when the former doesnt for some reason work out is remarkably smooth. Do you get into another relationship, to fill the void from the former , by doing the same things you did before or you start completly afresh? I don't think i will ever understand it, cause i have never been in a relationship, Maybe i should fall in love. The problem is the one i fall in love with always hapens to be straight!!!! well...well...