Their is no harm in having friendship with other women, even if you are in relationship. May be your girlfriend did not trust you, because of your previous behavior or any other cause, explain it to her that your relationship with other females is totally different, it is just a casual friendship and everybody needs few true friends in their life even if they have any BF or GF. Be honest and truthful to your self and towards your friends espescailly with your girl friend.
Regards,
sarah_9
Christian People Dating