Swimming is wonderfully meditative, quiet, and peaceful, but creating your own fitness motivation when cranking out the laps can be difficult.
If you find your love of the pool receding, it is time for a fitness switchup. I suggest you try a rocking group class like kickboxing. Your upper body will still take a beating (bad pun, I know), but you will be working your shoulders in a wider variety of motions, which is great for injury prevention. Jumping around on land is great for your bones since it's weight bearing, unlike swimming. Plus, being in a group class can buoy your waning motivation. The loud music and fun moves of kickboxing are certainly different, but are still complementary to your time in the pool.