Welcome to SI. You have been dealt a huge blow and recovering from this kind of trauma takes a long, long time.
Whether you R or D YOU will need to heal.There is no book, but I will tell you my opinion, take what you want from it and leave the rest. It will be based on my experience, because that's the only perspective I can give you.
You are not even a month from dday. Forget about "fixing" the marriage right now. You have been handed a raw deal and in the beginning it's about survival and navigating.
This affair is the burning building. He has gone NC and said he wants to commit to the marriage.
What needs to be done first is individual therapy. You get a therapist and so does he. Deal with the affair, the STI, the rage, fear and feelings that come along (how is it you got an STI from an EA?)
He needs his therapy to try and figure out what in him is broken. What made it ok for him to possibly throw away his family, wife and life for some ego strokes and attention? Where did he go that allowed him to trash his wedding vows?
The marriage is not to blame, nothing you did was to blame, this is all on him. If the marriage was so bad that he wanted out he should have left or come to you and discussed the situation. The answer is NOT to go outside the marriage and have an affair. Period.
He needs to own his actions. He needs to understand you will be going through hell for quite some time. You will wake up some days and love him and be thankful he is beside you and other days you will wake up and wish he were dead. You will love and hate him. It's all ok and any feelings you have are normal.
You need to accept the feelings as they come. Work through them, do not rug sweep and pretend everything is ok. I promise you, if you do, you will be back here in 1, 2 or 5 years asking what the eff happened.
He maybe saying he is sorry, but really, right now he is a liar and a cheater. His words mean nothing, promises....zilch. Actions matter right now, not words. Long term repetetive actions that support you and R, words will have meaning again eventually, but he needs to earn the trust back.
He needs to start and stay in his therapy and work his ass off trying to fix this, make what he did not hurt so much.
He needs to at the very least
#1. Be transparent.
All passwords, cell phones, email accounts...everything needs to be an open book. All bank accounts, everything. NO secrets. He has lost his "right" to privacy.
#2. Answer all questions, over and over again. Until you are done asking. And then he needs to be ready to answer them again. Without any anger, eye rolling, telling you to get over it ....
#3. Complete honesty.
Shouldn't need explaining...
#4. NC with the affair partner. No contact. She contacts him in any way, shape or form, he tells you immediately. He does not delete any emails she sends, answer any phone calls, respond to any texts...and he does NOT delete them without showing/telling you first. (her number and email should be blocked)
#5. Send a NC letter if he hasn't already.
#6. Give you a timeline of the affair, leaving out nothing, or giving you as much info as wanted.
#7. All "boys nights" should be over. An inventory of your friends should be done. Are they safe? Are they friends of the marriage and have your best interests at heart.
#8. Jump through hoops to do anything you need so you feel safe again, help you through this roller-coaster he has put you on. It is a long road, a hard road and he needs to have the ability to take your pain and carry it....until you are able to carry it with him.
The reason I believe you both need to put the marriage problems on hold right now, your life has changed as you know it. This affair is bigger than your marriage issues. You need to get your feet under-neath you before you try to address the marriage. You need 2 healthy, emotionally available people to have a healthy marriage. Right now the affair compromises your emotions and it needs to be in check before anything else can be done.
So, um that's a start
Really though, be good to you. Know that you do not have to R and making any decisions immediately aren't needed. If he doesn't get it (it is really too early to tell) if he doesn't do what you need you will need to be strong and stand up for yourself.
I know you want to R, I love R stories and hope everyone can make it through. Some can and some cannot. It's a personal journey and one you will have to navigate.
Listen to your gut.
Be prepared for bumps along the way.
Know that there are a ton of "issues" that can come up. Something does, come and ask us...one of us, if not many, will have already seen it or done it. We can help you navigate through this.
Know what your dealbreakers are and be prepared to draw your line in the sand. Sometimes you have to, sometimes you don't.
(((hugs))) you will get through this, just remember to deal with it, all of it. It is ugly and shitty, but it will ultimately make you strong as hell and if you both can do the work might just give you the marriage you have always wanted.