The most moving part for me was when Le Ly pleads with her husband to forgive himself, because she forgives him, and wants things to work out. And Steve is so gone by that point that he can only weep, ashamed of her strength and character. Both actors do an amazing job with the scene, and its outcome might be a bit predictable, but still very poignant.
of several moving poits i think that might be the number one.
Especially Le Ly's words: "I love the man I saw in Vietnam. I find you again. He's still there, Steve."
It was like she really found him, got in touch with real Steve. That led him to shoot himself as it was his only way (in his tormented mind) he could somehow redeem himself and set free the ones he loved. He just couldn't find a way out of the vietnam in his head.
Also that brings to my mind the scene earlier where she fell in love with Steve.
The moment she wakes Steve up from his nightmare and he kisses her. You can see at first kiss her face almost in terror (because of the raping earlier in her life), then she melts in his kisses and her face turns from being afraid into blissfulness, she have found the love of her life.