It's critical to maintain a bond with your spouse. Every unhappy couple I know has a terrible sex life, and while it can be a bit of a chicken and egg problem, a bad sex life and an unhappy marriage go hand-in-hand.
I suppose it's a bit more than just "sex life". Probably more like "Physical intimacy". As I've seen a few couples try to basically force "Sex twice a week" or something and that doesn't work at all. If sex becomes a chore, that might even be worse than celibacy, but neither are good. Both have to enjoy the physical company of each other.