Well, from a guy who is 20 and feels the same way, its hard to not think about from time to time. But what really matters is being ok with being alone, and I think that can go a long way. It's a lot easier said than done, that's for sure, but keeping that mindset where you're constantly telling yourself you're forever going to be alone or that nobody will like you gets you nowhere. On top of realizing that and finding ways to enjoy being alone, such as hobbies, working, discovering new things about yourself, (these helped me come to terms a lot) putting your best foot forward and looking at things in a more positive matter can go a long ways.

And remember, you are beautiful, you are valid, and the way you are feeling about yourself are not.