Decent-looking on my own, but feel horrid around beautiful people. How do I up my self-esteem?

I don't know why I let myself be so affected by how good others look. I'm pretty decent-looking on my own but I keep thinking, standing next to beautiful women just makes me feel really ugly. I don't know how to celebrate myself around others. How do I channel my confidence/beauty/self-esteem from within, rather than depend on an external environment? How can I do so in a more efficient manner? Thanks to anyone who can help.