As soon as I saw this node title I remembered two very different songs.
If I gave you present / would you try to exchange it?
- Ben Lee - Don't Leave
and
They call her name at 7:30
I pace around the parking lot
Then I walk down to buy her flowers
And sell some gifts that I got

- Brick by Ben Folds Five:

The latter song has always had the power, whatever my mood, to make me feel instantly sad. The guy in the song is in a bad situation, feeling crappy and obviously a bit low on funds.

Ketaset, your situation is probably different. For one thing it doesn't make me feel morose and no one is playing sweet slow melancholic piano music in the background. For another, selling your gift was (hopefully) not something you did because you needed the money. Although you say you'd never used the MP3 player I can understand why your girlfriend was upset. Admit it, it was a bit insensitive. What I don't understand is the huge reaction she had. This is really looking like it's going to break up your relationship? Blimey. That's a serious reaction to a rather minor offence. It's not like you were shagging her mum.

Perhaps you should have cleared it with her first. Your situation does have a bright side, by noding it you've brought the matter to the attention of your fellow nodes, who (myself included) will probably now think twice about selling gifts from loved ones.