OK, may I chime in. On a recent dive trip to Cabo I was paired with a diver, that once UW, I felt he didn't care one way or the other about the buddy system. He was on his own. It was a deep dive for me, a little over 100 ft. While doing the dive I noticed two teamed up partners, that were practicing very good, attentive buddy skills. When we got back on the boat, and lunch during our SI, I praised the two "good buddies" for how attentive they were to each other, hoping this might inspire my "buddy".
Well, on the second dive, my "buddy", was lost in space, going his own way, never looking behind to check on me. So I got close to the other two "good dive buddies", and they knew I was looking for support, and gave it. I was having trouble with too fast of an ascent, because I was leaning the wrong way for my dump valve and had to hold on to one, and he quickly signaled my problem with body english. I was able to regain control and hang with my new dive buddies for the duration of the dive.
So that's my story and I'm sticking to it. One dive buddy may not be worth a rat's you know what, and three dive buddies may help each other, me in this case.