Hey 15,
What a ride eh? Tangential issues raised and nit-picked to death, and little to answer your initial request, which is to help you deal with what you are going through now.
Well, to me, it looks like you have started on the correct foot in that you are going to IC, giving your BS full honesty (BJ & feelings for OM), and your actions show that you have remorse (custody issue).
You have already let go of the outcome of what happens to the M, which is in a way, a good thing. It indicates that you are not trying to manipulate the outcome anymore.
Is it correct to offer your BH full custody? IMO, no, at least not for the long-term, but I understand where that offer came from.
Correct me if I am wrong, but your thinking was that by offering full custody to your BH, you intended to show that you are now making yourself incredibly vulnerable to him, and that you are at his mercy.
With the BJ confession, it was giving your BH the unadulterated truth. To validate to him that his gut was right in that there was more.
The act itself was not the issue, but the giving up of that last nugget of truth was to give him the 'full truth'.
We can be pedantic and argue about specifics, but I see that you have done what BS would be looking for, in that you are now 'letting go' of controlling the outcome, and exhibiting true remorse.
As with anyone who has gone through life-changing experiences, one can sometimes over-compensate, and that seems to be what you have done/are doing.
Self-flagellating to the extent that you are doing, is over-doing it, but that is normal. We all tend to over-compensate when we are truly sorry for for something that we have done.
Is this the right behaviour? A definite NO for the long term.
If you continue with this self-flagellation for the long-term, you will not only destroy yourself, but it will affect your children's perception of you. You need to work on your mental health for the long term, and your kids need you.
Whether your relationship with your BH survives, or morphs into something else, you will need to focus on being healthy for your children. To guide them is their lives in a healthy manner. They will be depending on you to help them establish a healthy outlook in life; to have good boundaries, morals, and integrity.
You may ask, 'how can I, a cheater, liar, teach my kids about boundaries, morals, and integrity?'
Well, that will depend on whether you have learned from this tale of destruction. It will depend if you can pull yourself out of this shame spiral, and correct the toxic thoughts/behaviours.
So, first things first, get yourself into IC. You need it, your BH needs it, your children (especially) need it.
This journey is not for yourself, but for your children. Do not fall into selfish behaviour and thinking like you did in your A (I don't care about the pre-frontal cortex stuff as an excuse for bad behaviour) and take an easy way out.