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

Miley Cyrus – Wrecking Ball Lyrics on LyricsMode
No one ever quite knew who wanted who. And she's saying she thinks she nearly forced their relationship. She fell in love with him but came on to strong, all she wanted to do was break his quiet walls.
She threw herself into the relationship. She wanted it so bad. She felt like she needed it. It was different from her other relationships. And why she came in so hard, she thought she would be able to understand him more and he would be himself and let her in his life.
All she want is to break the barriers you put up. To be able to break in your circle but unexpectedly knock out myself in love with you who unfortunately doesn't want me. I came in like a wreaking ball. Wanting only to break your walls but instead created a great havoc inside me which lead me to breaking myself entirely when in the first place I only want you to open up and let me in.