Guilt-ridden Anxiety

Long story short: I cheated on my bf, he broke up with me the first time, but after a month, he decided he wanted to get back together and started courting me. I fell harder in love with him and we got back together for almost a year before he broke up with me again. He citing that he tried and couldn't forgive me, but in reality, he started an emotional relationship with a woman who started working at his place for 2 months.

During the month of July, I did things that I wasn't proud of, things that went against my nature, but the anxiety and the anger drove these actions; I saw his new passcode, got onto his phone and took pictures of some conversations he had with a mutual friend; I found her FB and *** page, took screenshots of those and sent them to his mom at her request; spoke to his brother about our situation; spoke to the mutual friend, who told me that my ex doesn't know that we had been speaking and if my ex finds out, he would NOT speak to the mutual friend at all because right now, he's the only person my ex is opening up to; I went into his email because he didn't change the pin on his computer and he's always logged in on his email to look through it and I found out how much debt he was in, told his mom who then told his brother and his brother said that he'll let it slide, but if I do it again, he won't hesitate to tell my ex what I did.

I basically cyber-stalked this woman because of what she did to my ex, how she initiated the relationship and how she's continuing it. I am feeling the guilt and anxiety because, like I said, I'm usually not this kind of person to have done all the above, and, to me, IF my ex comes back to me a 3rd time (I told him that I want it to be genuine and that we will have to go to couple counseling to work through out baggage and stuff), I feel like I should come clean about this. One friend is telling me to tell him whenever I want, WHEN I am not feeling this miserable and having these anxiety attacks and stuff; another friend is telling me to tell him this WHEN we start counseling, this way, there would be like an impartial 3rd party there; and another is telling me "let sleeping dogs lie".

Should I tell him WHILE he's in this relationship with this woman? (we are going no contact right now to give us both space to work through this stuff) Or should I tell him IF AND WHEN he breaks up with this woman and BEFORE he considers me again? Or should I tell him DURING couples counseling, IF we get back together?

The guilt is eating me and some days it's great where I HAVE to talk to someone about it while other days, it's not as bad that I can squish it down and not think too hard on it.