I had ED-E and Cass as my companions for a while, but I decided to go solo so I left them waiting in my home. After some days they returned to their respective origin places.
I lost the perk provided by ED-E so I decided to recruit it again, but when I went to John Nash's store it turned hostile and attacked everyone in the room. I tried to let it unconscious by shooting but I killed it instead, hence failing it's related mission.
I've read around the Internet about this behavior, it happens if you left ED-E "abandoned" for too long. But I can't find a way to make it join me again and not being hostile. Any help is appreciated.