bethw
If I may suggest. Before you do tell her, Think about what you need to achieve.
You are right, she deserves to know. But equally, there will be a number of shock factors.
That for 35 years, you have kept this inside. I strongly suspect that she knows, but has long since explained it away. This is the first wall you will need to break down.
The second is, what you hope to achieve. In your situation, I would aim for understanding. I would make it clear that, after 35 years I really need you to understand this. What we do about it is up to us. I have no plans or motives.
That will create the third wall. She will as herself the question, why now? A few years ago, some jealous relative suggested to my wife that my interest in one of our late teen nieces was more than uncle. It certainly wasn't, of course. She was late teens and having some problems. She wanted to talk. But my wife got herself into a mindset that I was a middle aged man, chasing my own youth by trying a (admittedly, very attractive), teenage girl. The problem is resolved now, thankfully. I certainly don't have and never did have any interest in teenage girls, other than to copy them!

The point I'm trying to make is that a lot of wives, especially when we get older, can fall back onto the 'losing his mind' excuse.
Then comes the fourth wall. What she thinks may be the consequences of what you are saying.
For this, I strongly suggest you think conservatively. Try to take her with you. Lonliness sucks.