My girl friend close with a guy friend

I am a Lesbian and my girl friend is straight. I am more like a tom boy and she loves me alot. She got this guy friend before we are in a relationship. Me, that guy and my girl friend was good friends before we are in relationship. But after we going out the closeness both of us has with him not anymore and it is natural. But my girl friend respects him alot, trust him alot, depend on him for a certain extent. The friendship she had with him and the friendship he had with her still the same. But it is so clear its not that much after we are in a relationship. All 3 of us working in the same office. And both of them works near each other in the same team. How ever the friendship she has with him bothers me alot, even though its not too much. But I feel she depends on him alot. But not sure whether I am right or wrong. For her he is like a brother and she always worry to make him hurt. And He twice told me that he likes her but hiding his feeling because she is not a christian so he cant marry a non-christian. So all in all the reason this bothers me so much, 1. Because I feel its natural to be Jealous or be upset. 2. I am just a tom boy and she is straight and I feel bad when she is close with that guy. Cos I feel I am not capable enough to give her all what she expects from a guy and yes it is true. Please Advice me and help me.