Holly,
I am a WS, and your story seems quite similar to mine -- two extremely drunken ONS, but separated by several years.
I haven't actually posted before (lurked for a while), but one thing in your post really struck me and I felt like I needed to speak to it.
This event has shaken me to the core - I am changed forever and my lifestyle is as well.
I told myself this exact thing after my first ONS, and I know that I truly believed it at the time. But time passes, and things may get back to what looks like "normal," and if you haven't actually done the hard work to look at yourself and your marriage and your "whys" then unfortunately, as I was, you will be vulnerable to this happening again.
After the second time, I confessed immediately to my wife, we started MC and IC, and I really began to look at the reasons I acted the way I did, the way I saw my marriage, and the things I needed to do to become a better person. It's hard work, and though I certainly would give anything to have come to where I/we are in our relationship via a different path, I am starting to feel good about myself and our marriage and what our future holds together.
Telling my wife about my infidelity was the hardest thing I've ever had to do in my life, bar none, but I decided that I had taken actions to put our relationship in jeopardy, and I didn't have the right to deny her the opportunity to decide what the consequences of my actions were going to be -- to me, that would be like cheating on her twice. I wanted to save my marriage, and I felt like there was no way that I could do that alone -- marriage takes two people; people who are honest with each other and who care about one another and who love each other.
I could not have healed myself without her knowing about my ONS, and if I didn't heal myself, then I knew I was always going to be putting my wife and her feelings at risk. Knowing what I know now, if I had to do it all over again a million times, I would always choose to confess to my wife. It hurt her deeply, and I was quite sure that our marriage would end as soon as she found out, but it didn't. She has told me that my honesty is probably what saved me -- and that if it had come out years down the road from somewhere else, it wouldn't have been the actual, physical cheating that would have broken the deal, but it would have been the years of dishonesty and the failure to face my own inner problems.
I won't judge you whatever you decide. I can't tell you what is right for you, or how your situation will play out, but I can tell you what was right for me, and that so far, it seems to be working out far better than I ever imagined that it could when I was where you are now. Only you can decide what is right in your case, but do know that I understand how you are feeling right now; I know it seems like the world is falling in around you and that hurting your spouse will only make it worse. I've been there. But for me, it started to get better when I came to terms with the fact that I screwed up and that the situation was no longer in my hands. It started to get better when I came clean to the person I swore to always be honest with, and when I started doing the real work (IC, MC, Owning, Helping my spouse through it, Working on myself), and I know I personally couldn't have done all of that alone...