If you say "I had a great day" then the implied question is "How was yours?" whether you say it or not.
If there was a specific "nice moment" with your daughter, or something funny on television, you could mention that specific thing.
Yes, best not to mention the affair or the other woman at all. If you do happen to meet them somewhere, then the most mature thing to do is to introduce yourself (if he doesn't introduce you). Refer to yourself as his "business partner" since that is true and likely to be least awkward for everyone.
I'm sure that you would prefer to scratch out her eyes, but that is not helpful.
