My wife knew from day 1 some 30 years of my TG leanings and even my experiments at transitioning. In fact she has said if she knew back then that we'd be going through this we'd never have gotten hitched. At least she knew why at times I was unmanly while others hyper-manly. It was actually the hyper, controling, always right, macho, etc. that would come out more and more over time and under stress that drove a wedge between us.
Four years ago after my third TG support group meeting I knew for sure I needed to be there. I also knew for sure I need to tell my wife what was going on. At the time our marriage was in shambles. I had lost my job, got another 350 miles away, visited her sort of montly or less since she didn't want me around, etc.. And throw in her being totally depressed to suicidal. A wonderful time to kick over the table. There has been plenty of tears shed by the two of us. Where things will wind up we'll figure out when we get there.
Tread slowly and try not to overwhelm her now that the flood gates are opened. Tons of very open and honest communication has kept my wife and I together. A new found skill on my part. SHe has always been pathologically honest as she puts it.
One simple overlooked lesson I'd like to pass on is "Avoid TMI". Us TG's have spent a lifetime barely getting a handle, at best, on this TG beast. An SO has had only minutes, hours, days, weeks or months. Only a lifetime of Jerry Springer and his sensationalizing ilk as a frame of reference. They have a ton of questions. Many they don't really want to hear the answer to. Others you yourself cannot fully or accurately answer. Especially at the start of this journey of self discovery. Some of us are slow learners to boot. I cannot answer the simple question of "Do you want to live full-time as Joanne?" after over 3 years and achieving my life long dream of being seen as and accepted as a female.
Every decision/choice in life has a cost. Something you are painfully aware of today. You just paid the cover charge, as had I and countless others. Only you can judge if the cost is worth the benefits gained.