Disclosure is a big thing. Read Ken Singer's article on disclosure and confrontation, it will give you an understanding. http://www.malesurvivor.org/Survivors/Adult%20Survivors/Articles/singer3.htm
Why does your therapist think you should tell your mother?
Is this something you think you should do and something you want to do?
Is there a need to tell your mother?
I haven't told my mother. I don't see the need or see any benefits, only pain that it will cause my mother.
Two weeks ago she asked me about my psychiatrist and psychologist. How I picked them and such. I mentioned I picked the psychologist partially because she did EMDR. Explaining what EMDR was, she asked me if they thought I saw something traumatic. Oops. I did manage to get out of the conversation without explaining that.
A year ago I laid the framework of disclosing to her. That was back when there appeared was a need to. Then I had filed charges against two of my abusers and it looked like the one was going to go to trial. It was better that it came from me than elsewhere. As it ended up, the one when brought in for questioning bragged to the detective about what he did to me. He had to be let go because of Statute of Limitations having had past. Thus the need to let my mother know no longer existed.
It's a big decision to disclose. Many factors to consider and lots of preparation.
You need to decide on your own what is best for you. Your therapist is a consultant for you, you are the one that is in charge of your healing.
Take care and be good to yourself,