My interpretation of the song:

You're obsessed with someone who is toxic and bad for your health, you know this but you can't do anything about it, over time you start to want that person even more, though you know you can't have them. You soon are swallowed by your own thoughts that you can't control, you can only think about what you did wrong and blame yourself for everything. You start to hate yourself and point out every flaw you have. Time comes to a stop when you begin to feel numb, you avoid people on purpose and your world is now grey. Realisation of the person you've become only breaks you down more. You've fallen so low you can't get back up. Nothing will be ok. From now on it's all down hill. It was never meant to turn out this way, but there you are walking towards the light just waiting to leave and finally be free.