1
general::
Phrase(s): take up with someone
to become close with someone; to become friends with someone. • I think that Albert may have taken up with the wrong people. • I did not want Lefty to take up with Max, but he did, and look where it’s gotten him.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Begin to associate with, consort with, as in She took up with a fast crowd. [Early 1600s]
American Heritage Idioms