Lyric discussion by -tear it up. 

Cover art for Walls lyrics by All Time Low

quite obviously about alex's girlfriend, lisa

Hey there, it's good to see you again It never felt right, calling this just friends I'm happy if you're happy with yourself

earlier on, they were on again/off again and it was an open relationship

Take off your shirt, your shoes Those skinny jeans I bought for you We're diving in There's nothing left to lose

this part seems like he's talking about when they decided to be together for real instead of open and they're diving into a relationship the taking off clothes part seems to add to the "diving" metaphor, like they're representing her inhibitions

I'm gonna break down these walls (Down these walls) I built around myself I wanna fall so in love (So in love) With you and no one else Could ever mean half as much To me as you do now

he wants to break down the walls he'd built up around his heart and finally let her in, so she's the only one, instead of the girls he'd been with before

Together we'll move on Just don't turn around Let the walls break down

he wants to move on from the open relationship, and he doesn't want to go back to what it was like before

I used to wear you like a ball and chain I'd run and hide at the call of my name It was obvious You were too much for me Oblivious I was young and horny

before, he felt like he was weighted down by her. he was "young and horny" and just wanted sex and not love

In retrospect, I wouldn't do it again Stop talking shit to every one of your friends I'm not the same boy you knew back then

looking back, he wouldn't have been in the open relationship or been a manwhore. she would tell all of her friends about that, but he's assuring her he's changed

I can't breathe My body's shaking You got a way With the way you take me 'Cause you break me down You know you break me down

this is the only part that i think is about sex (other than the young and horny bit), but it can also be taken as the way she makes him feel and how much he loves her; she breaks down his walls