Ok, sweetie, stop pitying yourself here, this guy did act like a sh*thead when he decided to leave and didnīt tell you anything about it. But donīt forget that he wanted out all the time and you didnīt let him go.
You are not worthless, but you are the wrong person for him. He didnīt feel happy with you and that makes *him* the wrong person for you.
Donīt date needy man, thereīs a difference between a man who loves you and a man who needs you. Needy people are selfish and self-absorbed, the last time they did anything for you usually is aeons away. They never bother about your problems, they have so many problems of their own. Stop believing that you are in this world in order to take care of a man. A man should want and not need you to solve his problems. You should support him, but itīs not your duty to give yourself up for one man. Because you also have a right to be happy and to be loved, not only your man.
You feel worthless, because all your self-confidence derives from the fact that your man is happy, when heīs not you feel like you have failed in your job. Donīt do this. Youīre more than this and thereīs more you can be proud of than the happiness of the man next to you.
I believe that in everyone thereīs a divine spark (even though Iīm not religious). Letīs call it something special in everybody that makes you unique and therefore not worthless. Youīre a living being with a consciousness, isnīt that great? Thereīs always more to yourself than you see, more than you want to believe, but itīs there. Right now youīre down, but Iīm convinced when you decide to leave the sadness and tackle your life and take responsibility for it instead of projecting your salvation on someone else, youīll be happy.
Start doing something for yourself, the advantage of not being in a relationship lie in a lot more time for yourself, indulge yourself in things you like. Consider all the great things you can do in the evening, because you donīt have to be considerate to someone else. You can do what you want. Ever wanted to learn something new? Nowīs the time to do so. Learn bellydancing (ok, thatīs what *I* want to do), learn a new language, take dancing classes, etc. These are great possibilities to meet new people and make new friends. The more people you meet the greater are the chances that you will meet someone that you really like and vice versa.
Iīll tell you the best "revenge" is to move on and show them how strong you are.
Go for it, itīs your life!