I am torn but I am going to go with NTA...

I was going to go with N-A-H because your boyfriend is rightfully confused, since this is not really a part of American culture. But I think his reaction to the point of wanting to leave is excessive.

People are saying you shouldn't have done this because he's American, but I'm not sure why you had to adjust to his cultural upbringing instead of him acclimating to yours? Being in America isn't enough of a reason; you still are born and raised wherever you're from and 2 years isn't that long of a time to suddenly just adopt any and all American customs and drop your own. Like, the argument could just as easily be made that he is dating someone of such and such a cultural background, and therefore this is something he should've anticipated. These slip-ups happen.

Your intention wasn't to embarrass him and it wasn't to be sexually intimate with your friend in front of him. I'd say that you did it so openly in front of him, if anything, shows how platonic it was. I'm not saying he is wrong to be confused and a little hurt, but to the point of demanding you dump your friend on the street or he leaves is very excessive. He could have at least talked with you about it and heard you out. But, you know, if you have any other customs/norms like this that would seem odd to him, you should probably tell him so he isn't so shocked in the future.