“I came in like a wrecking ball
I never hit so hard in love
All I wanted was to break your walls
All you ever did was wreck me”

Miley Cyrus – Wrecking Ball Lyrics on LyricsMode
She's stating her breaking heart once more, this time with a little anger.
She feel like she the only one trying in this relationship. All she wanted for him was the best and in return he give her the cold shoulder. She try her best to open up his wall but the more she try, the more she feel as if she in this relationship alone.
She felt that she was being shut out by her boyfriend so she came on him hard and she was starting to regret the whole relationship even if she still loved him more than anything she wouldn't be with him again because it doesn't matter if she loves him if he doesn't love her and keeps shutting her out.
She felt that the worst she would did was loving him faithfully but he was wreck it. He wreck her heart. And after all the she do he only replaces to break her heart.
So loving the person who doesn't loves you back maybe that's the worst but in her case, maybe it's different.