Before I told my wife, I had to think carefully about why I hadn't said anything to her. Because I knew that that would be one of her first questions, and she had a right to an answer.
I had certainly wondered for years if I was trans, even back before we met. But wondering isn't the same as knowing. Repeatedly, I had asked myself the question, and every time, the answer came back, No way. Of course, that was the wrong answer, motivated by internalized transphobia, but the fact remained that, for years, my answer that I believed was no.
So, when she asked the inevitable question, I was able to answer honestly that I had been in denial. That, in hindsight, I could see the signs going way back, and that I had wondered many times if I was trans, but that always, the answer came back no. And that that's how denial works, but I could deny it no longer.
I don't know if any of that applies to your situation. But it sounds like it's water under the bridge for you now. Don't beat yourself up over the past. You have to look forward now, not backwards.