While I can understand the context of that being a drug addiction, it depends upon the listener for the personal meaning to evolve, so here is my take;

"Baby's black balloon makes her fly, I almost fell into that hole in your life"

-- A balloon signifies elevation and some thing which has the potential to lift one to greater heights. However, it is black and relates to a black hole in her life; that which lifts her is as dark as what she is attempting to escape which I think could be isolation...isolating to cope with being isolated.

"You wern't thinking about tomorrow cause you were the same as me, but on your knees"

-- Both people were lonely but her circumstance was far different from his. He had the opportunity to change his life while, she did not, hence being on her knees.

"A thousand other boys could never reach you, how could I have been the one"

-- Another indication of the girl finding comfort in being alone and having never let anyone "in."

"I saw the world spin beneath you"

-- The world spinning beneath her illustrates that she appears to be both removed and standing still, not a part of the world and not making progress. She is at a "stand still" unable to find direction to navigate through. Next, is probably the most significant revelation which creates a better resolve for the context of the song.

" and shatter like ice from the spoon that was your womb"

-- Her world was cold and he watched as it shattered; a world in which the spoon that fed her was also the spoon that fed her children as well. If you see it from that perspective, the song could be about denied opportunities for affection as a consequence of tough decisions.

"Coming down the world turned over and angels fall without you there, I go on as you grow colder, are you someones prayer"

-- The balloon was not enough to lift them from the void, yet the world still turned 'round. He moves on and she stays in her cold world because she is someone elses prayer.

"You know the lies that others told you and the love you never knew"

-- She knows that those who have ever told her they loved her was a lie. Speaking and doing are two totally different things and she knows this, thus, has never "known" love.

"Or was it things they never showed you that swallowed the light from the sun inside your room"

-- Again, she found comfort in isolation and never knew any different, but over time the light she found alone flickered out. Perhaps his warmth showed her something that she had neglected to see and it forced her to realize what she was missing.

"And there's no time left for loosing, when you stand they forget"

-- Now that she if fully aware, she should stand firm and fight the battle instead of loose. However, when she tries to stand, "they forget..." the past. She looses either way. When she tries to stand for what she knows is true, the past has been forgotten and her stance becomes irrelevant though the damage has already been done. A cycle.
damage
"I go on I will lead you home and all because, I'll become what you became to me"

-- This shows that he is trying lead her "home" as in moving on from a world where she has no ground to stand and also moving on from him. He is encouraging her to heal and move on. He rebounded quickly as he was not in her same predicament but recognizes she had not done the same. She became a memory to him and he hopes that he will become the same.