I can understand some of you're worries, though I thankfully do not have a marriage to ruin. But I can tell you this, I could not hide who I am though I did try to not worry my parents, because my relationship with my father is troubling due to this.
In all honesty, a Gender Therapist would help you greatly, and you should also take a deep look in yourself. Think not of what may happen if you do transition, think only this "Can I live as a man for the rest of my life." Don't even bring anyone but you into the equation for now. If your answer is yes I can live as a man, well that's your choice. If your answer is, "I cannot live a lie." then I would say living as a man to save your marriage will just ruin it in the end anyway, for the real you will come exploding out of you eventually.
But that is totally up to you, its your life, your soul, and I think a Gender Therapist would help you out greatly. And not one of those "I wanna fix myself." Therapist, a supporting one that is actually looking after your mental health and not sticking to social norms.