To the OP, you are correct, the cause of the incident was the fault of both divers. Buddies should communicate between themselves frequently throughout a dive, keeping eachother abreast of their conditions. Becareful of getting so wrapped up in a dive or a task, that you don't know where your buddy is/ what they are doing. I had a diving buddy that has horrible (non- existant)
buddy & situational awareness (I'm being very nice about this). There are many that will not dive with him because of this. He has been known to leave a buddy & not even realize for a long time. Very quickly, diving with him, I learned that when I do a dive with him, that I am essentially doing a solo dive & plan the dive accordingly, on my part. He asked me to help him out with an Adv. Nitrox/ Deco course he was doing. We were doing a deep dive going up an old quarry haul road (gentle slope). It was briefed before the dive that there could be some drills pop up during the dive. About 15 min. into the dive, I gave him an OOA light signal & he continued to swim. I chased him (right behind him) for 50- 75 ft, signalling with my light the entire time, before I stopped & went "unresponsive". He continued to swim for a couple of minutes before realizing I was not there & returning. I was originally going to make him take me to the surface as an unresponsive diver, but he ran into me with such force, I had to move to keep from getting completely clobbered. I aborted the dive at that point. When we got to the surface, I said nothing to him. He came up with an excuse that there was no way I could have been out of air at that point in the dive, so there was no reason for him to look back & check on me (he was leading the dive, per the plan). I still said nothing. After doffing our gear, he asked me if I was pissed. I asked him to get my phone for me. I then instructed him to call our instructor & my parents & tell them that he "killed" me because of his inattention. That seemed to make something in his head finally connect. After that episode, his situational/ buddy awareness improved vastly. He now checks back & constantly looks for signals.
BTW- Good job at keeping things together & getting the 2 of you safely to the surface.:blinking: