Maintain Your Self-Respect
Regardless of how anyone else values you, you still have the ability to maintain your self-respect. Anyone who sincerely works on being a good person has virtues that make him valuable.
Never judge yourself based on anyone else's opinion of you. Ultimately it is your mind which determines how you will consider yourself. Even if you rely on someone else's judgment, it should be your own conscious choice.
Develop an objective view of your strengths and weaknesses. Work on growth and improvement. At the same time, realize that your intrinsic value is innate and can never be taken away from you.