I think HouseOfPlane nailed it here.
WGOI, you’ve been heard.
Right now you are not in control, she is. She has something that you want, and that puts her in control. If you want it desperately, that puts her an even more control.
So how do you take back control? You do it by giving yourself a choice. At a minimum you have three choices, you can continue to live in pain, you can deeply accept that you won’t know the full truth and stop rolling in the manure of the affair, or you can divorce. You control these choices completely, she has no play in it.
Right now the easiest path, and by that I mean, the one that takes the least work, is to just live in pain. The alternatives are so much harder to achieve that they don’t even feel like a choice.You should fix that.
The way to fix it is to aggressively move towards a divorce. See a lawyer, understand your rights, understand the possible outcomes, and draw up the papers. Do this even if you don’t want a divorce, because what you really wanna do is you wanna give yourself choice.
When you are now sitting on the fence, when you put yourself in a position that it is just as easy to jump back into the marriage as it is to move towards a divorce, or to just stay on the fence watching and waiting, then you are in complete control. You know that whichever path you now choose it was your choice.
Work to put yourself in the position mentally where you are OK staying or going. Where you can ask your wife questions, and if she doesn’t answer the questions that’s OK because you are OK going. Again, you are in control.
Sending strength!
You need to regain control, and moving toward divorce, whether you talk to a lawyer or even file for divorce, doesn't mean you HAVE to get divorced, but it will send the message that you're not messing around and you're not going to take it anymore. She needs to come clean and talk to you about it if there's any chance at fixing this and helping you heal. If she's unwilling to do that, then it should give you an indication that she might not love you or respect you enough to tell you the truth and give you what you need to work through this. If that ends up being the case, is she someone you even want to be with?
In either case, taking some action and drawing a line in the sand will at least give you some sense of control back. Rug sweeping, as you've done for the last several years, almost never works out in these situations. Whatever happens, I hope the best for you, man. I know the pain you're feeling right now and it really, really sucks.