bc,
On such an issue I think you should get strategic about things. By that I mean you should ask yourself some questions: What do you want from telling your mother? What are you likely to gain if she responds positively? What will you lose if she reacts in a bad way? What is she likely to do once she has this information?
Disclosure is important. Ultimately we all need to be able to break the silence and speak out - to someone. But in the first stages we should seek out safe people whom we think will understand and support us. It's also a good idea to plan a bit: let's choose a time and place that will offer some opportunity for communication. A hectic family visit where privacy is likely to be very limited might not provide that opportunity.
One thing that concerns me in your post is this:
My relationship with everyone has never been one where I spill my guts.
Do you mean here that no one you know cares enough about you to listen to your needs and problems? Is that likely to be true? Or do you mean something like this: "I can't ask for what I want and need because I never feel like my needs and concerns are important. Or if they are, and I express them, they will never be met."
This problem is so common among survivors, and of course it's something an abused boy learns early on. His needs for love, safety and protection are meaningless, or if they do have meaning, all that can be cancelled out for the sake of the sexual satisfaction of a predator. That's not a lesson the boy is likely to forget, even though it's an absolutely false lesson. It's something that's burned into his heart, and he will carry it on into adulthood unless the wound is healed early.
One of the greatest feelings in recovery I have had so far came with the discovery (at age 56!) that I mattered, that my needs were important, and that I had a right to ask for them to be met. I hope you will work towards these same goals. But for now, I would say try to limit your efforts to contacts with people who are likely to respond with genuine support and concern.
Much love,
Larry