I don't know what "faithful friend" means to you, it reminds me of dogs. My friends are those I enjoy being with and who enjoy being with me, usually because we have similar interests unrelated to our "work". Yes I have coworkers who are friends but we became friends because of proximity and after I retired the friendship has lessened extensively, even with similar interests. We never were in the same "group" together, our lifestyles were established and different and where we lived, worked, etc. was different later. I suppose if one lives in a small town and sees one's T often outside of therapy in similar pursuits, that might make a friendship more likely but I am reminded of my stepsister seeing her OB/GYN at a party, it's just very awkward because there isn't an even start and it's quite possible, because of that, that things could go horribly wrong.

If I were your T and became your friend, there's always the possibility that we'd be in a group/public setting and I'd say something offhand to/about you that would reveal something you would think was too personal and not something you wanted others to know. The line between what is learned as a T working with someone and what is experienced as a friend would get blurry for a T and there would always be the feeling I had to check myself to make sure "Did I know this beforehand from the intense work with Goingtogetthere or is this something "general" that one would learn as a friend?"

You will never have the opportunity to choose to not reveal because you already have. You will always be at personal disadvantage to your T, who can choose what she reveals about herself. T can be a friend but you will always have been your T's client. It's like becoming friends with one's parent. Yes, you grow up and are an adult, have children of your own, but you are still always 20-some years behind in development and always the child to your parent's parenting.

I'm not saying you are or would make a poor friend are not "worthy" in some way but friendship is pretty much a peer relationship and you can't be your T's peer. I read an example of a T and client-who-became-a-T's friendship and it took 20 years to get there. I do not know what you are expecting from being a friend of your T but I think either it will be more of a good acquaintance thing where maybe you have lunch together once a month and befriend each other on Facebook or it will not get very far before your T decides she should end it for herself and it does not go well with you/you get hurt.