Try going to Lansdowne. It's nearby, gives you the full spirit of mountains. Peaceful and chill vibes. And on your way, near Kotdwara you will find Rasta Café. You'd love the ambience and food of the place.
You have many options near delhi for your special day celebrations( N i'm sure, you must be looking for something very special with your partner). Go and celebrate it in Agra- Taj mahal, as this is for you and your loved one. So, nothing suits best than travelling to a place which is itself a "symbol of love" in world! It is beautiful and certainly perfect for occasion. Have a memorable journey as well as celebration. Enjoy!