not the only fish in the sea
Also, lots or plenty of good fish in the sea; not the only pebble on the beach. Plenty of other suitable persons, especially for a romantic relationship. For example, When Bob walked out on Sally, all we could tell her was that he was not the only fish in the sea, or Bill knew she wasn't the only pebble on the beach but he was determined to win her over. Both fish and pebble here refer to something available in large quantities. The expressions using fish have been used to comfort jilted lovers since the early 1500s. The variant using pebble was first recorded in a poem of 1896 by Henry Braistead: "If you want to win her hand Let the maiden understand That she's not the only pebble on the beach."