と一緒にいた

was with

→ と
phrase Rare #28,158
was with と marks the person someone was with; 一緒にいた means “was together.”
JA: 昨日は友達と一緒にいた。
EN: I was with a friend yesterday.

昨日の夜は、トムと一緒にいたよ。

I was with Tom last night.

その時トムは誰かと一緒にいたの?

Was Tom with someone at that time?

ヒョンソと一緒にいたのか?

Were you with Hyeonso?

— グエムル -漢江の怪物- (2006)

昨日の午後、トムと一緒にいた?

Were you with Tom yesterday afternoon?

彼女と一緒にいた人たちは誰だろう?

I wonder who the people with her were.

お前は金田と一緒にいた…

You were with Kaneda…

— AKIRA (1988)

あの夜って、トムと一緒にいた?

Were you with Tom that night?