BH here fully reconciled 8 years past Dday. Just so you understand my point of view.
Right now the biggest thing you can do to help him is to answer all questions fully and honestly even if they hurt him or you. Never deviate from full and complete honesty about everything from now.
He is still in shock and will need a lot of space. It is good he is seeing an IC. He needs to understand that your A was about you and had nothing to do with him. Anytime he bring that up correct him.
At present he has a lot of questions. Those questions will get deeper and less superficial. The answers you have today are not the "real" why. If you stop there you are not only robbing him of the answers he seeks, but also the growth available to you after making such damaging choices.
I get that you don't understand it right now and that is ok, for awhile. You need to begin to dig deeper into some painful stuff from your past to fully understand the pull that the A gave you.
"I wanted to because I am selfish, bad, cruel, etc." That is a shortcut to the real reasons why your character deficit allowed the choice of the A to be made.
Those are the answers you have know and those are fine today, but they also point out that you are an inherently bad person at your core. All the optimism in the world will not repair you and your M without you getting very deep into the brokenness that still exists in you today.
When my W told me she was "bad," or that I "deserved someone better," all it did was make me hopeless that the M could be saved. The absolute worst thing for you, if your goal is to R, is for your H to agree with you. Right now he is clinging to the M because it was his safe place before and it is familiar and/or comfortable. Even with all the added pain. It is what he knows. Familiar and safe are not the same thing.
What he needs to see is that you are changing. That you have fixed whatever broken parts you have and are up to the task of becoming someone that would give him the best chance at a very bright future.
You know what doesn't lend itself to a bright future ? The idea that you are selfish, entitled and "bad." Don't put thought into his head that likely will develop on their own. Show him why your are different and that you are willing to make amends, even if that means he needs to leave the M.
Find the real why you gave yourself permission to do this and then gently help him understand and see why it wouldn't happen again.
This is early in the game. You will need a lot more stamina and perseverance if you intend to become healed and further to give your second M a chance.
Right now he is in shock. He likely hasn't shown you any real feelings about your choice to have an A. Once those emotions surface you will need to be in a better place yourself emotionally so you can support him.
He might may act out, make threats, tell you things that are very hurtful. He needs to let those things out and you need to fully understand the impacts your decisions have had on him. I'll say again, fully understand, what this has done to him. We are talking years, not weeks or even months. This is a trauma like no other. It takes a lot of time using the right tools to recover.
If you aren't up to the task ( I know you say you are, but you are still early in the game) the kindest thing would be to let him go and find someone else that would make him happy.
A lot of people will tell you that forgiveness is the goal and what you need to seek. Forgiveness comes with a very high price to any betrayed spouse. If that is what you want you have to earn his grace and atone for the wrongs you have done to the M. I would avoid MC at the present and both of you work on yourselves.
No shortcuts here. You get through infidelity, never around it.