"Take up with" is a phrasal verb that means to begin a romantic relationship or friendship with someone. Some synonyms for "take up with" include "get involved with," "start seeing," "begin hanging out with," and "forge a bond with." Other similar phrases that can be used in place of "take up with" include "take a liking to," "befriend," "associate with," and "form a connection with." It's important to note that each of these synonyms may carry slightly different connotations, so it's important to choose the one that best fits the context in which it's being used.