There are literally thousands of famous quotes about love. From Shakespeare to the Bible, there's no shortage of sayings to choose from if you want to go with a tried and true sentiment. Quotes may be considered a little on the predictable side, but sometimes the words of others may be the only way to communicate what's in your heart.
Look for something short (so it'll fit on your band) and sweet. If the two if you tend to wax philosophical, why not quote Plato, who said, "At the touch of love, everyone becomes a poet." If you're both art fans, you can cite Pablo Picasso, who said, "Love is the greatest refreshment in life." It doesn't really matter what quote you decide to use, however, as long as it matters to the two of you.