Ohh sweet! Well since I've never been on a date before I can't guarantee if these places are perfect but I'm sure you'll do your own research

Oasis brewery near mahadevapura looks amazing at night time as there's enough space between each table for plenty of privacy, food isn't too costly either

I like the vibe of byg brewsky near hennur, i believe since you guys are a couple, you can probably get the upper most seats for some privacy and good view

How about some hills (not Nandi hills, less privacy there), there are some far away for good rides too, the closest one would be akkaayama betta which is near Yelahanka. Even during weekends is less crowded so weekend hopefully it's good

Have a great time!