take up with (one)
To form a close relationship with or begin to associate or keep company with one. Often used in reference to an unsavory or untrustworthy person or group of people. He was a great student until he took up with a group of troublemakers and ended up getting expelled.
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.
take up with
Begin to associate with, consort with, as in She took up with a fast crowd. [Early 1600s]
take up with
Informal To begin to associate with; consort with: took up with a fast crowd.