That maternal transference hurts, but it's okay, you're not a weirdo for feeling that.
That therapists leave/move/end all the time, so be prepared for that.
That it's hard to tell the truth to the therapist on the first day when you don't even know her, but it's even harder to tell her the truth when you've been lying about something for a long time.
Therapy is a two-way relationship, even though it doesn't seem like it.
You will come into therapy expecting to talk about one or two things, but you will learn that another problem you have is actually much more important or that you have problems you didn't even know about.