Hey Mary -- You definitely are not alone, there seem to be many here who understand your pain.
My wife has known about my gender confusion from the very start, so there were no surprises ... until I recently started exploring 'going all the way.' It's been rocky, for sure, but we took things very slow and deliberately, and let her digest the big picture (ie -- life with me, and life without me).
I asked her to read Jennifer Boylan's "She's Not There," which is the best, most accessible book on gender confusion I know. In it, Boylan's wife deals with the incredible mixed emotions of a gender transition, but decides to stay out of love. Your wife may decide the same. If not, perhaps it's best to (painfully) part, but get it over with.
The guilt is there, yes, but it's assuaged by the fact that this is not really a choice. My wife understands that, and so does not 'blame' me. Hopefully your situation will be similar.
And the slowness of the process has been a blessing. It has allowed both of us to process this whole thing without feeling like we're jumping irrationally into anything.
Hang in there. Love will out.