"Why did he killed my heart like that?" Killed is odd :P
Very sweet ending :), true that :P
Emotional poem, you got the feel try put in some expressions in. Like the first stanza "your heart broke to million pieces", How was your facial expression when he left without a goodbye? How does it feel if your heart stops beating? compare it to something.
"I shall never forget the pain" What kind of pain, How does it feel, How agonizing is it? the senses :P use them in poetry, sight, touch, feel, hear etc. hehe