The girl I love has a boyfriend. How I get her?

If this girl is currently in a relationship, don't attempt to interfere. You're only expressing immaturity by stepping in between the two of them, and that is very unattractive. Find something or someone else... it'll keep you occupied, and maybe even give you that amazing love! Just remember, there are plenty of fish in the sea; never rush love!

You don't get her. Get your own female. She is unavailable to you.