Why? you ask...I'm not going to go there Honey, because whatever I say is going to come across as an excuse for my actions...there is none.
I compliment you on your timing, IC. *sigh* Nothing that cries "double bind" as loudly as a spouse admitting to a ONS while undergoing chemo. There's a clean, self-righteous anger that a BS has every right to feel that your wife won't ever be able to feel when she needs it most, which is now. And just before Christmas, too. *double sigh*
Yes, it's good that you fessed up now. But you WILL have to go into the "why", even though you rightly say there is no real excuse for it. Tell her the "why" you believed then. And why the same why won't happen again, because .... fillintheblank.
You can't just skip over the explaining, dear. Sorry.