I think having a GF or BF has become a casual thing that comes with little thought and responsibility.
The truth is, having a girlfriend means getting into a relationship where you take care of her, converse with her day in day out, basically share you life with her.
If it is just the rush of sexual appeal, the romantic thrill, the convenient companionship, I think you have the wrong idea. This type of sincerity won't last long but sadly it's the type people seek, get disappointed with, but still go searching for it because of the convenience.
I think it is easy to agree that to find that "one" whom we are willing to invest our time, sincerity, and lives with is no easy task. Even if we find someone the relationship isn't guaranteed to formulate and maybe for this reason we look for the convenient alternative.
I think the solution is not easy to find, but if you are convinced that a relationship should be something more deeper than a casual fling, maybe we need to start living up to those standards and be more cautious in whom we choose.