the married man is asking this woman (i'm assuming not his wife, LOL) to join him for a social event because:
1. his wife can't be shown in public for a variety of reasons.
2. he wants to show off this woman in a social event to show off his sexual prowess.
3. he is interested in this woman beyond the typical bang-bang-bye-bye relationship and wants to see her in a broader environment to observe her while making mental notes about what he does or doesn't like about this woman before plunging into a relationship that would be more (not sure how much more) than pure lust. what kind of event is it? black tie? casual? wedding? seminar? fund raiser? the event may also help explain his motives.
Actually it's very risky to meet other people as some people in that groups know about his wife. He made up some reasons to take her (which is very logic) for that event so wife no have doubt when someone reporting back to her.
The social event for lunch gathering where bussiness people meet eachother.