Don't judge her by her words, judge her by her actions. Your gf sounds confused. Have her FB messages said she loves someone else AFTER she said she loved you?
You need to figure out if she is still confused now that she's with you, or she was just lonely that one time when she told the other guy on FB she loved him.
People often confuse infatuation with love. Be careful not to make decisions based wholly on emotions. It usually ends up very badly.
I have a long time interest in psychology, specializing in relationship dynamics for 30 years.
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