Selena Gomez - The Heart Wants What It Wants Lyrics Meaning

When I was on, when I was on stage and I was thinking of...
I felt like I know, I know him though
And I know that, and I know his heart
And I know what he wouldn't do to hurt me
But I didn't realize that I-I-I feeling so confident
Feeling so great about myself
And then it just be completely shattered
By one thing, by something so stupid
But then you make me feel crazy
You make me feel like it's my fault
I was in pain