I'm jealous...?

It is disturbing when your bf is friends with a girl that he feels he can share anything with and talks to her about these things instead of or before talking to you. Its understandable that you're jealous. But, would you be jealous if she was a guy? You said it yourself. He sees her as nothing more than a friend. If its bothering you to the point that you overthink it, you should have a talk with your bf or both your bf and this girl and maybe tell them about your feelings, or at least part of what you're feeling. If your bf is telling this girl about his relationship problems, or is going to her for advice before asking you what you think, let him know that it makes you uncomfortable, and that, as his gf, you would like to know whats going on in his life before this girl does. And, if hes talking about relationship issues, let him know that you're not comfortable with him airing your dirty laundry, even to people that are friends.