I think it's perfectly fine not to share this info with your T, should you decide to do so. I, for one, however, go to therapy just because it's the one place I can be me- no lies/makeups/whatever- just me: the good and the bad stuff. I need to learn how to accept myself (love would be great, but let's be real here) so this is how therapy works for me. So if I were in your place I'd tell.

I do wonder, however, about all the keep it to yourself advice- if ppl truly believed that this is absolutely OK to do, why not tell your T?
I do believe telling your T would help you ease your mind, Mactastic. A good T should know how to handle this- no way you're his first client who have done so.