hard to comment on that situation when we're not in it and don't know exactely what went on inside their relationship. I do have a hard time thinking she has no strength - she's obviously felt safe enough to cheat on him, and involve the children in the "triangle". And since he knows you've vacationed together - she was strong enough to let him know about it. So from what you've said - he's not the only one at fault.
and you'll have to define what a cowadice is
