To get someone back [I prefer, "Getting someone back"]

One of my friends is trying to take [She is not his property or an inanimate object] get his girlfriend back. I tell told him that it's a lost cause. He did bad things was not nice to her when they was were dating. her and So she breaked up broke off their relationship because she won´t didn't want to be duped by empty promisses.

But now However, he realized now that he's a new man and he´s decided to take have her back. I hope he'll win this his cause. Actually, I really think if he's sincere, in his feelings she'll let bygones be bygones. She used to be crazy about him and he'll make the effort have to prove his love.

If I were the girl, no matter how sincere he is, I won't have him back.  If she was so crazy about him once upon a time, she had tasted how hurt he can be towards her.  She had seen him in his ugly state that he is able to inflict on her.  What guarantee she has that he won't treat her the same in the future.  "Once bitten twice shy" is the English saying and the Chinese equivalent is "Once seen a ghost, always be afraid of the dark".  Unfortunately, the vase has been cracked, no matter how much it is mended, one knows there are cracks in it.

Of course, he has to move mountains to prove his worth and how much true love there was in her.