How is “be mixed up with” used?

In Heat (1995), one line is: “Why did I get mixed up with her?”

Which movie is “be mixed up with” from?

The clip at the top of this page is from Heat (1995).

Why did I get mixed up with her?

3 作品で登場 · 1 本目

to be / become friendly with or involved with sb that other people do not approve of

5 本の映画に登場

オックスフォード映画の 100%
to be / become friendly with or involved with sb that other people do not approve of
Why would a son of old Linus get mixed up with a man like Mike King?

定義：Oxford Advanced Learner's Dictionary 第 9 版