I'm not sure I have an answer, but one day after six years with my current therapist, I suddenly had an overwhelming desire to tell her that I loved her. It never even occurred to me before that moment, but when I happened, I just had to do it.

It wasn't at all immature or fleeting. (I don't know why, but I feel like I need to say that.) I'd had a mom similar to yours growing up, and for me it wasn't only that I felt she didn't love me but--what I realized when I realized I loved my T--was that my actual mom never made it OK to love her.

It was hard, really hard, telling T that I loved her. Given my past, I was extremely afraid she'd find me repulsive or not accept my love or something. But it was the most healing thing to be able to tell her and to have her react positively.

Anyway, I don't know if it's at all the same for you, but maybe the need to tell your T has something to do with unfulfilled love in your relationship with your mother?