I used to be good at analyzing poetry, so here we go:
I think it's about how she's become his baggage. He's hurt her, but now he's stuck with the fact that she was a part of his life, even though it's over. He knows that he can still get in her head, because he knows her so well. But now he doesn't have that kind of control over her, and instead, he's kind of forced himself into an obsession with her. He knows that's what she wanted all along from him, but he was too busy controlling her before, so it's kind of a bitter love.
Like a firework unexploded
Wanting life but never
knowing how