I my playstyle is inconsistent

I have a chess teacher that helps me analyze my games and show what mistakes I am making. Anyways, we sometimes play games together, and against him I play amazingly well. Even when he's looking at how I play when I'm playing against someone else, I'm playing amazingly well. However, without the presence of him, my skill level drops down drastically. How do I play well without the presence of him?

Are you sure he isn't just telling you that you're playing well? Do you feel nervous when playing without him there?  By playing more people without the presence of your teacher and getting used to it you will play better . The skill level of the people you play against when with or without him could be a factor aswell .

Maybe having him there makes you try harder in order to impress?

Are the other games you are talking about all online? If so, it might just be the difference in having a physical set in front of you, and a real live opponent across the board.

I don't feel nervous at all, I just feel unfocused and make incredible blunders.

He uses the exact same program as I do and with him I can usually beat a 1900 but without I can barely beat a 1400. He doesn't tell me what moves I should make, I play out the game myself and he just watches.

1900 and 1400 are huge differences , even if you are playing off 1 hour of sleep you should be able to beat a 1400 if you are able to beat 1900s . By program you mean the same training program? Also what are the circumstances for the different games ? online , Over the board , tournament , etc . Maybe post a game where you were with your coach and another where you were not so there is a better idea .