Probably.Did he really have to confess after 15 years??
The insidious cancer of the cheating had finally eaten away enough of his resolve to continue the lie, I'm guessing. Good for him, in that sense. Should have come clean at the outset, or avoided the affair altogether, but what's done is done.
IMO, confession is always the best option, if one foot has already gone down the ugly path. She needn't have attempted murder. Had he suspected that, perhaps he should have left her, then put it in a memo. Might have been safer, that way.
But, for me the breach of trust is one of the things that is absolutely verboten. Tough to repair, once done.