Maybe it's just because I'm a guy, but I would have been more direct, and expected an answer straightaway. Yeah, your timing sucked, but given that you asked, what was the point of not asking for an immediate answer? It sounds to me like you may have to ask again, or slowly drive yourself nuts waiting (nah, you wouldn't do that!). From everything you've been writing lately, you already know that it's very unlikely that he's in contact with her. In all probability, you would have gotten the answer that you wanted, and could have quickly changed the subject to a happier one, thereby saving the rest of the evening. Anyway, water under the bridge.
Admittedly, my thinking is being colored by my own situation. I'm currently struggling with whether or not to confront my W about her "secret" cellphone, which I'm sure is being used to continue contact with the OG. (Sage, LL, others, c'mon over to my thread if you have a chance).
Anyway, asking once every 3 months is hardly too often. DBing demands that we be solution-oriented, temporarily setting aside our own needs and desires in order to rebuild our M's; it doesn't demand that we never have our needs satisfied (like the need, yes the NEED, to have the any-contact-with-the-OW question answered).