Who was Bobby Orr's defense partner?

Al Sims was one towards the end of his Boston stay I imagine there's a whole lot more, not forgetting he was with Chicago as well.

As I think someone has already said, Orr played with lots of people. Here are a few sites talking about his playing with Dallas Smith:
http://bruinslegends.blogspot.com/2012/01/dallas-smith.html
https://bleacherreport.com/articles/1706863-ranking-the-five-best-defensive-pairings-in-boston-bruins-history%23slide5%20
(see #5)

Here's a site talking about Al Sims playing with Orr:
https://icehockey.fandom.com/wiki/Al_Sims

I think Bobby even played with Brad Park for a while before Orr retired.

I think it was mainly Dallas Smith, who put in 861 appearances from 1965 through 1977, against 631 by Orr during much of the same period. However, he would probably at some time have accompanied some of the Boston Bruins' other giants of defense such as Ted Green, Mike Milbury and Brad Park.
https://en.wikipedia.org/wiki/Dallas_Smith_(ice_hockey)

Below is an excerpt from the article which the link refers:

Dallas Smith was a muscular stay-at-home defensemen as Bobby Orr's
defensive partner, allowing Orr to play his offinsive game between
1966 and 1977.....

[from eagletribune.com 2002 article, no longer online]

1. Don Awrey A defence partner variously to Ted Green and Bobby Orr, Awrey once went 153 games without scoring a goal.
https://www.nhl.com/news/don-awrey-symbol-of-grit-for-boston-bruins-alumni-at-stanley-cup-final/c-307569520

2. Dallas Smith (Hamiota MB), later Bobby Orr's defence partner with the Bruins https://icehockey.fandom.com/wiki/Dallas_Smith

3. Wildcat scout Peter Nevin, who was Bobby Orr's defence partner with the major junior Oshawa Generals https://www.eliteprospects.com/player/772392/peter-nevin

I don't know of this will help or not.
The Bruins had to get over the loss of hard-nosed defenseman Ted Green, whose
skull was fractured in a pre-season, stick-swinging incident with St. Louis
forward Wayne Maki, by filling that gap with stay-at-homers like Don Awrey,
Rick Smith and Gary Doak while Dallas Smith teamed with Orr. See:
https://archive.org/stream/Sports-Illustrated-1969-10-13/Sports-Illustrated-1969-10-13_djvu.txt