go out with
phrasal verb.to spend time with someone because you are in a romantic relationship with them.
phrasal verb.to be involved in a romantic or dating relationship with another person; an intransitive phrasal verb requiring a prepositional object.
“Is he still going out with Sarah?”
“They started going out with each other after meeting at a friend's wedding last summer.”
“Although they had been going out with one another for several years, they decided to remain friends rather than pursue a formal engagement.”
always followed by 'with' when the partner is mentioned; 'go out' alone can mean to leave the house for social reasons.
contrast with 'go out' (socializing generally) to avoid confusion; note that 'dating' is a more modern, often American-leaning synonym.
the preposition 'with' is required to link the verb to the person being dated.