As your grandmother told you whenever you despaired over a particular guy, "There are plenty more fish in the sea." That's certainly true, but not all of them are fish you can catch, and wasting your time pursuing a dead end (or fish) is a surefire way to end up hurt, frustrated, and disillusioned. This is not only a bad use of your time, it can put you in a mindset that will actively repel the very best men, the ones you ultimately want to be with, because you may come across as negative and jaded.
The good news is that if you're in a good emotional state, the men you repel generally aren't the men you ought to be with anyway. The bad news is that if you are in a place where you need to work on yourself, then you might be pushing away the best men - the kind, smart ones who know how to treat you respectfully whether your relationship lasts a night or a lifetime. Either way, it's important to evaluate your situation so as to get the best out of it now and figure out whether you need to be working more on yourself or simply on your man radar. So let's see which of the plenty of fish you won't be catching anytime soon!