What does the song Desperado by the Eagles mean?

Recently, my family went on a day trip to those outdoor market. We saw one of the tent with all those beautiful carved out iPhone case. My uncle told me to pick one that symbolizes my life. He picked the case that is carved out like a card, queen of heart. My cousin and I were really confuse about why he picked the case because we all know he hates gambling. He told us that he picked it because of the song Desperado by his favorite band. " the queen of hearts is always your best bet" When I listen to the whole song, the music is really calm and I love it, but I have no idea what it means… Why did they write it?

The queen of hearts reference in that song has nothing to do with gambling. The song is about someone who apparently can't settle down and find true love. "Don't you draw the queen of diamonds, boy She'll beat you if she's able; you know the queen of hearts is always your best bet…" It's about the kind of female companion this person should and shouldn't seek.
The use of metaphors, imagery, comparisons (similes), analogies etc, is very common in lyrics.