What do you do if the girl you like has a boyfriend?

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There's this girl that I met recently and I've developed strong feelings for her but, conveniently, she has a boyfriend. They seem happy together judging by the way she talks about him, his family, and their facebook pictures together so it doesn't seem like they'll be breaking up soon. Part of me wants to be glad that she's happy but the other part wishes that they would break up. Has anyone been in a situation similar to this and how did you deal with it? Your help is greatly appreciated.