Honesty is an admerable trait.
Tell her about it and you might gain some points, or you could lose a few, but I dont think she will break up about it if you told her (though it is still possible).
Though if she finds out from someone elce, you will lose ALOT of points, and you might break up depending on her, and how well you apologise.
Plus if you hide it, it will probaly eat at you until you tell her.
The sooner you tell her, the better.

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