As humans we have to grow. We either grow together or apart, there's no standing still.
We have three kids - 13, 9 & 4 and as the mom, it is very rarely that I feel guilty for our weekly date night. Everyone has their needs met throughout the week and mom & dad spending time together is a necessity, not a luxury. They have grown up with us having our time & is just part of our routine. I think they are at the point where they enjoy when we go out. We always come home laughing and refreshed - we are better parents because we are happy and secure. We are creating a solid foundation.
It is a balance. We give our kids everything to make certain they are happy & secure. When we take care of our relationship, we are modeling the importance of tending to the foundation of our family. We are providing the kids with the tools they will need as they become adults entering into their own relationships, and that's not something to feel guilty about.
My parents had "bill day." Who gets excited about paying bills? It wasn't until I was married that I understood why. They would go out to lunch, pay bills, shop & only they know what else. All I know is that no one was allowed to go with them & they came home (late), happy. They were married for 55 years until a sudden passing. They had "their day" for as long as I can remember. Along with unconditional love, it is one of the most important things I learned from them.
The kids are going to grow up and move out & you'll be stuck with your partner so you might as well make certain that they are your best friend from the start. It is much easier to maintain something than to try and fix it once it is broken.