I don't know anything about this girl's stress but you?YOU obviously have to deal with stress also!
The ex just shows up and then she is considering breaking up with you!
I think it was normal to get angry after her. What were you supposed to do? Sit and say ok fine I still love you so much?!
Don't blame yourself.
You seem not to be the first in her eyes...Sorry to say this but how in the world have you been selfish?
You deserve a girl who puts you first.