a game of mine, what could have black done?

Well in this game, I think the queen was let out too early and White took advantage of the unprotected, centralized queen and the undefended king.

Bringing out the queen so early I find is never a good idea.

Oh yeah.  That queen move is never a good idea.  The only person that works against is someone who doesn't know chess at all.  Keep the lady at home until the othe pieces are developed.

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 Agreed. This way, when all of the other pieces are gone, you can do very good things with the queen, if you know what I mean!! ;D

Early queen move was a problem.

But black could have avoided early mate by moving 8..Be7 .There could be a few other moves as well.

the queen was moved too early and my advice is that you don't move the queen unless you can do something useful with it

Once he gobbled the e-pawn he was doomed.  Before then I'd say things were pretty close 7.Be6. followed by a queen side castle at some point and things would have looked tight.

Unless you can calculate more than 3 moves+ ahead yes it is unwise to bring the queen out early.

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2...exd5