The phrase "dwell on" generally means to focus or linger on a particular topic or emotion. However, there are several synonyms that can be used in its place. For instance, one can say "fixate on", which means to become obsessive about a certain thought or idea. Similarly, "obsess over" can be used to describe someone who is unable to let go of a certain subject. "Brood over" can be used to convey a sense of deep contemplation or worry, while "ponder" suggests a more thoughtful and reflective approach. Finally, "ruminate" implies a prolonged and deliberate examination of a topic or personal experience. It is important to use the right synonym to accurately convey the intended meaning.