If you are asking yourself if your relationship has gotten boring, it has. The question is, what have you done to expand your own horizon. Learned a new language? Signed up for a dance class? Read any stimulating books lately?
Start with yourself first. Your partner will be motivated to catch up with his/her fascinating partner. Be the inspiration. Do something once a week other than watching TV together. Schedule a new activity bi-monthly. Discover events in your community. Go to a farmers market or an art museum. Listen to a live band. Visit a town nearby that you've never seen before. The list is endless.
Explore. Be creative.
On the flip side, couples need to maintain their own hobbies/activities without insisting the other come your event. Smothering behavior is not attractive. If you love live theater and your partner hates it, for instance, go with a mutual friend who enjoys it as much as you do. Obviously, you can indulge your partner once or twice a year. Your significant other might enjoy a single baseball game while you go to a dozen more every season.
Two independent personalities blend more happily when boundaries are respected. Keep your identity in tact. After all, that's why you fell in love with in the first place!