My Girl Friend Is Talking To A Lesbein?

Me and my girl friend been going out for a year.The other day a lesbein added her on myspace they keep talking back and forth.The lesbein asked my girl if shes bi or lesbein she said no i have a boy friend.I think there just friends i hope.The lesbein commented her picture saying mmmm your hot.It buged me i told the lesbein leave my girl friend alone she did shes afaird of me.My girl friend denyed everythimg I thinking of brakeing up with her what should i do?