What I am sorry you're reaching that conclusion but if your H doesn't do anything to fix it I do believe you're taking the right decision.
I am now reading "How can I ever trust you again" and I can't digest everything but a lot is helping me. I am not certain what stage I am at I seem to be moving between stages a lot.
Sometimes (and much more than before) I feel I am numb and don't care much what is going to happen. Others I see hope of a better, stronger marriage. My H is doing everything right, instinctually which for me is a good sign but of course from time to time would say something stupid like "I want us to move on and focus on us and rebuilding what I fucked up". I then explain that so do I, that's what I am doing. In all honesty I do have moments when I am so angry that I am stuck. I seem to focus on little details that now bother me like the text he sent her to instate no contact and telling her it's over which I have read and said it is ok to send but now (11 weeks later) don't satisfy me anymore. Like he said I've decided to give my marriage another chance. That is flipping driving me crazy. He had no fucking decision, he was begging for chances from me at that point and promising me he'll to everything in his power to fix it. Sometimes I get fixated on something like that and cannot snap out of it. The text, I got fixated on it yesterday. Luckily he did the right thing and said to me something along the lines of "I can see this isn't helping you to progress, let's call her now and I can arrange a meeting and I can tell her face to face that I had no decision to make, that I was begging for chances, that she was a mistake and I only love you". Obviously I denied that it is a good idea to contact her and asked him not to do such thing but his willingness to do it helped me snap out of it.
I'm not sure we'll survive this as frankly there's no guarantee that's not a deal breaker for me. But I want at this point to be able to tell my kids that I did give him a chance. He's not a repeat offender and (as far as I can know) this is his first affair after so many years of marriage. There's no excuse to it (as I found out going around in circles about the why) and he knows if we survive there won't be another chance.
The reality I came to accept is that my trust is ruined not only in him but in all relationships so if I'd meet somebody else I'd live with the same baggage. Not because I don't believe that people can be faithful at all but because what we had in our marriage was a connection and a match that was close to perfection and then this happened. So I won't ever be able to believe that should I meet another man he'd be faithful to me.
I also became quite realistic about it (and I don't expect people to agree with me) and I started to believe that given the right circumstances and vulnerabilities everybody is capable of cheating because the consequences are not thought of at all. I know I didn't cheat but I came close to it a while ago, when all that stopped me was in fact the age of the guy, he was 10 years younger.
No I don't make excuses for my H and I am still not sure I'll be able to reconcile and recover our marriage. I am giving it a go because life isn't always black and white. I just know by his reactions that he didn't think of any of the consequences and now facing them he's shocked himself that it was him who did that.
For the man I used to know for so many years I think I am willing to take a risk and see where that takes me.
One thing is for sure, I am not the same person, I've changed and he needs to change himself and understand who is this person who surfaced and was willing to risk it all an ultimately what brought into his life, what gap it filled and is that gap now gone?
What helped me in the last few days was writing down a plan should I find out anything new at any time (this includes another affair in the past, him still being in touch with the ow, more important details about this affair and obviously another affair in the future). Then I discussed these with him and he knows what my plan is step by step. Down to visitation rights for the kids for example. This makes me feel in control.
Good luck to you all and I hope we all grow stronger by the day no matter the path we choose.