So just when you think you're close enough to be brothers
They wanna come back and cut your throat when you ain't looking
from Eminem – If I Had Lyrics on Rap Genius
Meaning
It definitely seems that Em is speaking from experience here. Most likely he has had some unfaithful friends in his life.
To help improve the meaning of these lyrics, visit "If I Had" by Eminem Lyrics and leave a comment on the lyrics box