Since you don't know the area that well there's a lot for you to do. We do season tickets at Theater Three in Dallas some years, other years we subscribe to another venue. But I really like Theater Three. It's in the Quadrangle, near lots of small, very good restaurants and getting out to see an affordable play (the prices for season tickets are great), is very nice and very much adult time together.
In Lewisville there's a little theater on Main Street, just before Mill Street. Don't know the name, but it has good offerings too.
Then there are the high-school plays... Flower Mound High School and Marcus High School theaters are great. Not like when I was in high-school. Just go to the school websites, click on performing arts, theater and hopefully you'll find it.
Other than plays... there's plenty of clubs... I love the concerts at House of Blues. There's also museums and plenty of places to eat.
Also in Flower Mound, if you haven't discovered Little Pete's on Lake Grapevine, it's kind of fun when they have live music. The food isn't great, but not awful, but the drinks and appetizers are what you go for...
Grapevine has Wilhoites, if you want to go to a biker bar, but don't eat there. Drink.
Also in Grapevine, the Lancater Theater or Palace Theater (the same, just not sure what they call it now) has live music and old movies, check the schedule. Good places to eat in Grapevine.... Ama Lur inside the Gaylord Texan. And any of the many other restaurants in Grapevine.
Southlake... good place to get-away while staying near. The Hilton at Southlake is right there, you can eat, drink, see a movie and walk back to the hotel. Brio's is great italian food. Go for happy hour for cheap appetizers.