My interpretation is that "I'm fighting sleep right now" is presumably about deep thoughts not allowing him to sleep. "I walked through the thickness of your heart... I wrote the melody that brought you back to life, love" means that he was in a relationship with a girl who had been badly hurt before and his love brought her back to life and healed her wounds. "Who says we're wrong for opening the wrong doors?" Is a rhetorical question that he doesn't want answering, it's all part of the experience. "Lock up - swallow the key, you'll never replace me" this rhyme shows that he thinks that she's made a big mistake by ending their relationship and she won't ever replace their relationship. The line "We've all fallen for someone we're wrong for" shows that he accepts they were not right for each other and wants to move on. Her "weakling anti-bodies" were previously unable to stand up for herself up until this relationship, which ties into him bringing her "back to life". "I fell like Jack for Jill and you came tumbling after" - he fell for her quickly but she took her time to fall for him much more carefully. She's careful and she stands "up for herself". The next bit is a little ambiguous as it's a little bit muddled, that they both blame themselves "You're blaming all this on yourself BUT the photograph that's on your shelf is a younger, dumber version of myself". This shows that they've been in a long term relationship and that the split is mutual, not just her fault. "Back then I told you if you fall I'll fall too" - they loved each other but "lock up swallow the key, you'll never replace me". Meaning that she can get a better relationship than this, perhaps because she left him for something more that he doesn't believe is possible.
Beautiful song and I did my best with this interpretation!
My interpretation is that "I'm fighting sleep right now" is presumably about deep thoughts not allowing him to sleep. "I walked through the thickness of your heart... I wrote the melody that brought you back to life, love" means that he was in a relationship with a girl who had been badly hurt before and his love brought her back to life and healed her wounds. "Who says we're wrong for opening the wrong doors?" Is a rhetorical question that he doesn't want answering, it's all part of the experience. "Lock up - swallow the key, you'll never replace me" this rhyme shows that he thinks that she's made a big mistake by ending their relationship and she won't ever replace their relationship. The line "We've all fallen for someone we're wrong for" shows that he accepts they were not right for each other and wants to move on. Her "weakling anti-bodies" were previously unable to stand up for herself up until this relationship, which ties into him bringing her "back to life". "I fell like Jack for Jill and you came tumbling after" - he fell for her quickly but she took her time to fall for him much more carefully. She's careful and she stands "up for herself". The next bit is a little ambiguous as it's a little bit muddled, that they both blame themselves "You're blaming all this on yourself BUT the photograph that's on your shelf is a younger, dumber version of myself". This shows that they've been in a long term relationship and that the split is mutual, not just her fault. "Back then I told you if you fall I'll fall too" - they loved each other but "lock up swallow the key, you'll never replace me". Meaning that she can get a better relationship than this, perhaps because she left him for something more that he doesn't believe is possible.
Beautiful song and I did my best with this interpretation!