Bedfellow

noun

1. One with whom one shares a bed.
2. An associate, often an otherwise improbable one.

   "1873 They say that "misfortune makes men acquainted with strange bedfellows". The old hereditary Whig Cabinet ministers must, no doubt, by this time have learned to feel themselves at home with strange neighbours at their elbows. — Anthony Trollope, Phineas Redux, Chapter 40."