sometimes giving each other more space might be just what you need. do you ever ask how to keep your friendship with normal friends fresh? no. cause we usually give friends alot of space. In the same manner, you cld ask yourself if the two of you need to give each other more space. Space to hang out with other friends more, with family, etc... and not do everything together 24/7.
Of course, at times, there is also the need to try something new together. I suggest that you think of something that you are interested to try but never done before or seldom do. And go do it together.
But at the end of the day, all stable relationships will settle into some kind of rhythm. And its absolutely normal, and you just need to enjoy the times together for what they are, a precious companion to go through the boring routines of life together. Hope this helps.