21 is still young dude you've got forever to build a new awesome life for yourself
Main thing is to focus on being happy about you, and your life, not just because you do or dont have a girl. Placing your happiness on something outside of yourself and your zone of control means that you are giving up your own control and responsibility for how you feel.
Set yourself a ton of goals and start working on them immediately, even if you only take small steps.
Is there anything specific you are looking to learn?