I have PMd you some stuff that might help you, OP.
The others are right - it is very early days. It is also true that your H won't yet understand all the thought processes and what things meant for some time.
However, I wanted to pick up on a couple of points. I may have said this on your original thread, but if he came to you after the affair was underway to tell you that he had grievances with your relationship, it is an astonishingly common manipulative trick, that even he might not have acknowledged he was doing at the time. It is so common in infidelity cases that I have coined it the "setting you up to fail" moment. This is is sometimes motivated by an unfaithful spouse needing to have an excuse for their imminent or continued infidelity, to give "fair warning" that the marriage is in peril or to have a convenient "I told you things were bad" excuse on discovery.
In reality, your H had absolutely no intention to improve your relationship by having this chat and all the efforts expected by him were going to be yours. I bet you'll recall that this conversation didn't include the efforts he would make to revitalise your marriage - and I bet you'll recall that in fact his efforts and attention worsened. That nothing you did in response to that chat seemed to make any difference.
If that chat had truly represented an honest attempt to improve your marriage, your H would have shared the responsibility, he would have obviously told the truth about his affair and the efforts you made would have been matched by his.
If he didn't come to you before he met the OW to say he was unhappy with your marriage, then I'm going to suggest that he wasn't unhappy at all. In more cases than you'd imagine, an affair causes marital unhappiness, not the other way around.
The only difference this time around (after your youngest's birth) was that he had the opportunity and the lifestyle that permitted it. You had the most enormous trust default too and infidelity was the last thing you would have suspected. I expect he thought that this was a fairly risk-free adventure when it started out - and didn't think it would cause the devastation it has.
I hope you get a good counsellor and don't have to wait too long. In the meantime, it will be helpful to keep up the lines of communication and talking. He really should read that book.
You might find it helpful to time-limit your conversations, but ensure you have them every day or so. Don't be afraid to take time out when your anger or upset overwhelms you. Don't be be afraid of your anger either - it's a really healthy, galvanising emotion, as long as it doesn't harm you and as long as it doesn't have the effect of making your H clam up and with-hold information you need to hear. The truth, although horrendously painful at times, needs to come out and ultimately, it will liberate you, because your imagination will be far worse.
But do bear in mind that people in the midst of an affair very often tell as many lies to themselves as they do to others. The truth he believes now might be very different a year on from now, when more distance and objectivity provides hindsight.
I'm going to give you an example of something that might be apposite. During the affair, your H might have told himself that this was just about sex and it was therefore not threatening to your marriage. He may have believed he was compartmentalising the two worlds successfully. However, in reality he might have actually been what Shirley Glass calls a monogamous infidel, of which there are various shades.
At the most extreme end, the monogamous infidel cannot share intimacy with two people and the attachment to the affair partner is so great that having sex with one's spouse is regarded as the greater infidelity. At the other extreme, the person cannot share sexual and romantic intimacies with an affair partner if he keeps up the strong connection to the spouse he has always previously adored. He has no strong emotional attachment to the affair partner, but he literally cannot have an affair with someone else while there is a strong connection to his spouse, so he seeks to reduce it to allow the affair partner in, if only for a short time.
People in this latter category often speak of how marital intimacy would feel "unfair" to their wives, or receiving love and affection from the spouse they are betraying would feel "wrong somehow". At one end of this continuum therefore, the attachment to the affair partner is greater, at the other, the spousal connection is stronger, but what provides the common denominator is that monogamous infidels cannot compartmentalise to save their lives.
This is often subconscious, especially the latter extreme, but what the person is completely oblivious to is the damage this is causing to his marriage, because it becomes obvious that there is a disconnection, even if the trusting spouse doesn't know why. Usually, she will blame it on work stresses and so will he, if confronted. Some of that, he will even believe himself, because he simply won't confront that he isn't compartmentalising this at all, in reality.
On discovery, it is sometimes only when the recovering couple share their stories; the individual and very different stories of the past 9 months in your case, that greater understanding is achieved. Your H would really benefit from hearing what your life has been like for the past 9 months. One of the best things you can do to prepare yourself for that conversation therefore is to re-construct the story of your life since last summer, only this time with the information you now have. Betrayed spouses often have a compelling need to fill the gap in their life history - to accurately record a chapter of their life when they were being deceived.
It is part of the process that Shirley Glass discusses when she suggest you co-construct the story of the affair and what life was really like for each of the protagonists in the triangle - and the collateral effects on others, such as the DCs, friends and extended family members.
Your H might therefore be lying to himself in part when he says this was a sex-only affair, but I suspect some of this is also to spare your feelings and to minimise his own culpability and how much he risked. It can be a slow process with lots of denials and battles, but it might need to start with you giving your H permission to be honest about any feelings he had for the OW and how they reduced towards you in inverse proportions, as a result.
As you will see from the Shirley Glass book and the stories, many people find some peace when they finally settle on a version of events that makes sense, both in terms of the evidence all before them - and their knowledge of their partner and his attachment style. Many people are able to forgive their partner having infatuation-type feelings for someone else, or even very strong feelings, because it accords with what they know about their partner and is often more permissible and understandable in the end than someone who was a compartmentaliser and utterly devoid of feelings or kindness towards the woman he was having sex with.