I would like to talk and befriend you.
Just tell her as there is no point in living a lie especially with your girlfriend. If you're not sure you're gay, consider telling your girlfriend about your feelings without labeling yourself. If you're sexually attracted to two genders or sexes then you're bi even if you prefer one over the other. However, even if you do possess an attraction to males, if you are bisexual and still feel truly aroused by your girlfriend, a heterosexual relationship could totally work for you.
You have nothing to be ashamed of.