Great advice so far. I'd like to add this...
BREATHE
Seriously, just allow yourself a little time and a little grace to see what happens. You are SO early in this process, and if you don't mind a personal observation, you seem panicky as hell. Not that you don't have a right or a reason to be, but right now, it is doing you no good, and leading to even more poorly thought out decisions and reactions. You made enough bad decisions when you chose to cheat. Let's not repeat those same practices now, okay?
Has she left the relationship yet? If not, why do you think that is? Doesn't she, as the victim here, have every right and reason in the whole world to dump you and go live her life however she chooses? And yet her choice, thus far anyway, is to try and R? What I'm trying to say here is this... If she has the willingness and the desire to try and make it work, despite the undeserved and overwhelming pain she is in, then what is your excuse for leaving? You've barely even started and you are already discussing throwing in the towel! Do that, and yes you free her from wasting her time and life reconnecting with a cheater AND a quitter. But that also means that YOU do not improve. And so nothing will change. You will not change. In that case, there is nothing stopping you from continuing to be an untrustworthy and unsafe person, for yourself and others. It honestly fixes nothing, it is yet one more dodge of accountability and responsibility. I know this is just my opinion, but it seems like you owe her more than that. You kicked her to the curb every time you had an affair... now when the time comes to put in the effort and show her you are more than that... don't make her feel tossed aside again. How horrible to put the thought in her head that she is unlovable and unworthy, and then to spike that thought in deep by giving up without any real, sustained, consistent effort. Even if you don't think you owe it to her for some reason, you should at least owe yourself a better life.
The following is an exact quote from a letter my wife wrote to me. She said it well, and I think it is something that you need to ask yourself.
This journey never ends. It is perpetual for as long as we are on the right side of the dirt. How do you want to be remembered? Do you want folks to say, poor guy, he had his demons even though he tried? Or do you want folks to say I want to emulate him because despite the horrific adversity he faced and the years it haunted him, he made us all look up to him? He is someone that I wish I could be.
Who do you want to be Josh? Not for her, not for me or anyone else, who do YOU want to be? And why aren't you BEING that person?
Here is a little exercise I'd like to suggest for you. Get a piece of paper and a pen(cil). Make two columns. Label one column, "WHO I AM" and the other column, "WHO I AM NOT". And then fill in the columns honestly. Go as far as you need to. Mine ended up being a few pages long :) Do not restrict your columns to just infidelity! This is about ALL of you.
e.g. I AM a generous person
I AM good at my job
I AM trustworthy with money
I AM someone who cheats on his spouse
I AM creative
I AM NOT a thief
I AM NOT honest with others at all times
I AM NOT someone who thinks of others when making a decision
I AM NOT able to take care of myself without help
When you are done, you have a blueprint of yourself, of who you are, today, right now.
Now, what are you not happy about with your blueprint? For example, if you wrote, "I am not an honest person", are you happy with being that way? If not, then... what are you going to do about it?
If you wrote, "I am someone who cheats on his spouse", are you okay with that? Are you proud of being that person? If not, then... what are you going to do about it?
Go through it, and start to make changes. You don't have to change all at once, but change what you can, when you can. Some will be easier than others. But all are worth it. And when you are done making those changes in your life, you WILL be someone you like more, someone you love more, and someone you respect more. And as a special added bonus, you will also be giving your spouse some possible reasons for staying. Nothing changes if nothing changes. So change.
Common experience says that it takes 2-5 years just to begin the process of R. You are how far in? Again, give yourself some grace and some time. Some things in this world take TIME and EFFORT to heal, and you can't substitute, diminish or eliminate either of those things. So set some goals and make some effort, and you will feel better about yourself, and the whole situation, when you have something to hang your hat on that you are proud of. Now go be someone better.