I periodically take breaks from UO myself. It's not that it's less fun, although it is less fun, don't get me wrong - but rather, too much of a good thing will always get stale after awhile. Take a break, maybe for a couple months, maybe for a year. Eventually, you'll return with fresh eyes again.
The people you play with can make all the difference between boredom, and fun as well. Get to know them on a deeper level and eventually you'll find a reason to return more often. At least, that's the way it is with me.