He texted the woman saying he didn't believe she has showed me something so bad I would be so upset and accusing him of cheating (he did it in front of me); sshe answered back with all the texts they had exchanged.
He had no way of hiding it and was "forced" to read them in front of me, finally admitting that, though they were not sexually involved, that WAS cheating.
I came on to him with everything I had (calmly) and told him what I had to tell him, including that he had helped ruin a marriage and had made the 3 of us miserable; that the least he could do was take responsibility for that and be ashamed of himself. He tried to defend himself as much as he could but but then cracked, cried his eyes out, apologized...
Needless to say that I told him that I'm sorry I'm leaving without a speck of respect for him, especially once he always claimed to be as transparent as glass and as pure as snow..

Note: he claimed he didn't remember having written that. Amnesia is a bitch!