Yay! You sound like me! I've never expressed my feelings to friends or family but will say "I love you" back. I found that when I told some friends about my therapy, they said how much more open I was to them. That, I guess, gave them "permission" or allowed them to feel more comfortable telling me their feelings towards me. It has been very eye opening/healing/etc. So, just like you, I felt if I say this to FRIENDS, why wouldn't T. fall in that category.
I remember last summer feeling in love with her but my mind never wanted to admit/say I love her. It's like it's couldn't connect the two or something. Then, about 2 months ago I left her office feeling and knowing that I loved her. It was the first time I guess my mind allowed it? Anyway, the next session I told her I loved her and then quickly looked away. She asked me why it was so hard to say. I said I don't need or expect to hear it back - I can just tell the way she looks at me. She nodded and grinned and said something about showing it vs saying it.
Yay! We've made progress! We are supposed to try out things on our T. so we can go out in the world and practice our change. For me, that means actually telling my T. my feelings without fear so telling her this was a huge step. I haven't said it since and actually went through a period of regretting it. I still haven't said it first to a friend and one friend said she can't wait for the day when I do.