"Find that IC ASAP. For you, for your M, and for your family!"
I suggest also: Find the very best one. And humbly talk again to that monk in the caves.

"I can't believe I am writing this... I never thought he could do it, "
And coming from someone who persistently supported you leaving him.

"I sense I am playing with fire and I wil push him away ..."
You sensed this 2 years ago too, if I remember right.

Given he is open to talking with you would it help to get honest answers to the following questions, maybe helped by IC, but this may be too traumatic for you just now, when you also need a lot of TLC.
- What did the OW have that you didn't?
- Why did he ditch her and come back to you?
- Why do you still want him back?
- If he didn't come back would you want him back?
- If you left him for the other guy what would it be like?
- What does it take to forgive him?
- Is OW to blame or is it 100% H to blame for getting involved with her?
- Can you take responsibility for any of this mess?
- Is he willing to eradicate his character flaws?
- Do you really know the devastation D causes?