Perhaps its a bit literal of me, but I'm thinking that this song is about closing yourself off to love and all it's pain. But then just as you least expect it, and no matter how hard you try to fight it, someone comes along and breaks down the walls that you found yourself building around your heart. "My heart's crippled by the vein that I keep on closing. You cut me open and I keep bleeding..." its like saying that despite the fact that you've been closed off for so long, and no matter how you try to fight the feeling, it's there. And it doesn't seem to end.