"You are somewhere in the attic
Looking something close to tragic
Dating t-shirts and your mattress
I'm floating on the stairwell
With my toes grazed in the cedar
Thinking softly would a tender box leave them in...":
To me, this means the girl he loves is kind of a lost, tragic mess that's alone, and he wants to go and save her.
"And what a flammable heart I've been given":
He has a heart that sparks a relationship between he and a girl.
"You can be in several different places, I am sensing your location":
He is thinking about her a lot, even when she's gone
"You are somewhere in the basement
Beating on a makeshift drum kit
Songs that I can hardly stomach
I'm floating on the stairwell
With my fingers shaking frantic
Thinking softly what a concrete mess we live in...":
He broke up with her, he hears songs that remind him of her, he can't stand the concrete mess of the world he lives in because he is so sad it ended between he and the girl.
"What an icebox heart i've been given":
He feels he has a cold heart for breaking up with her.
"I am to starting to sense your location
In an alternate dimension
In a country side of England
Spirits trapped inside the linens
And you're feeling quite at home there
Also feeling somewhat lonely
No one sees you in your pixelated fish nets
And your black and orange beret":
He is "sensing her location" aka, thinking about her. He is coming up with ideas of where she is (alternate dimension, country side of England) what she is doing/how she is feeling (quite at home there, but also missing him too) and how life is living without her. He is still thinking about her even though life is moving on.
"Oh please believe the ghost in me
Is doing what I can to find you out":
Somewhere deep down inside, he wants her back and misses her.
"You are somewhere in the attic Looking something close to tragic Dating t-shirts and your mattress I'm floating on the stairwell With my toes grazed in the cedar Thinking softly would a tender box leave them in...": To me, this means the girl he loves is kind of a lost, tragic mess that's alone, and he wants to go and save her.
"And what a flammable heart I've been given": He has a heart that sparks a relationship between he and a girl.
"You can be in several different places, I am sensing your location": He is thinking about her a lot, even when she's gone
"You are somewhere in the basement Beating on a makeshift drum kit Songs that I can hardly stomach I'm floating on the stairwell With my fingers shaking frantic Thinking softly what a concrete mess we live in...": He broke up with her, he hears songs that remind him of her, he can't stand the concrete mess of the world he lives in because he is so sad it ended between he and the girl.
"What an icebox heart i've been given": He feels he has a cold heart for breaking up with her.
"I am to starting to sense your location In an alternate dimension In a country side of England Spirits trapped inside the linens And you're feeling quite at home there Also feeling somewhat lonely No one sees you in your pixelated fish nets And your black and orange beret": He is "sensing her location" aka, thinking about her. He is coming up with ideas of where she is (alternate dimension, country side of England) what she is doing/how she is feeling (quite at home there, but also missing him too) and how life is living without her. He is still thinking about her even though life is moving on.
"Oh please believe the ghost in me Is doing what I can to find you out": Somewhere deep down inside, he wants her back and misses her.