AFWAW, I'll chime in here - my W is in an affair. I have done the old "I'll-never-date-I'm-married" thing as well. The deal is that I WON'T date while I'm married - I respect marriage too much.
But, there is a "special person" that I have been talking a lot too, and the kids have started talking about (because they like her and her kids) and W has been informed by them that we are going to do stuff as play dates.
I didn't realize what an impact it would have - W has made it a point to not really say anything to me - and she is sort of ho-hum about the affair (kind of funny actually). Ever since she found out about this other woman, she has been going all ga-ga over OM. She also called me and said she wanted to come be with us this weekend at a fun thing at their school - up til now she has completely avoided ANYTHING that was family time.
I just have to chuckle - I am just friends with this woman, and have zero plans to date or anything. I haven't been jealous at all of W and OM - just hate what it's doing to our kids and family. But when the tables are turned, things start happening.
Seriously, you don't have to lie - but if she says you should date, just say, "OK". If she is surprised, and presses you on it, just say, "We'll see". Be vague, and watch her go nuts. But, I cannot stress this enough, do NOT change until you see real changes from her. I went dark on my W for a month - and she started pursuing me. Didn't see OM for a month. I started responding, and talking to her, and a couple weeks later, it was back on with OM. Until she admits to wrong-doing, seeks help, commits to the right thing, and so on, you don't budge.
Trust me on this - here's the best part. If it drives her AWAY from you, then she's not in the right place, and isn't be ready.