Probably on most days, my favorite movie of all time.
De Niro didn't or was unwilling break his personal code in the end, first, he chose the criminal value system and his own code of loyalty, over his own his heart, and then, he walked away, that is the real heartbreaking moment, for both of them. As she looks out the window, after waiting, getting more and more confused, scared, regretful, she is in so far over her head, then, hope, as he appears. He turns away, and shatters her hopes and heart in that scene.
"There's no point in me going anywhere now, if it isn't with you"
I may have used a version of that linerecently with my Ebie, damn.