I think he's killing himself over a girl. She said she loved him, but she's broken his heart plenty of times. "another boy without a sharper knife"; he didn't quite kill himself. "Can I even complicate your breathing, I guess I'm just your average boy"; he isn't anything special to her. He wants to "try a new life" without her. I'm not sure what the "Awkward stranger" part means. Overall, she's killing him inside, but he can't live without her, or with her. It's a live-hate thing. She's a drug. He loves her more than she would ever love him, and he can't live knowing that.