Where is the location of fawkes on fallout 3? 10 points whoever can answer this question!?

Ok, I've been playing this game for a while. And i already had butch as a follower, but when I got captured by the enclave in vault 87, he wasn't there. And when i got outside of raven rock, fawkes was there. My karma was too low to get him. And i followed him forever! he eventually stood at "abandoned car fort." so i went to go give a hobo purified water for some good karma. And i went back to the car fort and he wasn't there? could anyone tell me the location of fawkes? And since i had butch as a follower back then, where is he gonna be now?? 10 points!