If this guy not following you back is enough to lower your self-esteem, then your self-esteem is about as durable as a china doll being used as a football.
I get liking someone, I do! And I haven't forgotten about angst/exaggeration. I would say, though, that many a truth is said in jest.
Cultivate interests, and that includes not just things that make you feel good, but things which you can accomplish and feel good about.
Unfortunately, the world is full of situations where you're snubbed. Knowing your own personal value, and not depending it on anyone's judgment, attention, or opinion will help you combat this.
<Insert obligatory statement that I am not a doctor>