I should've known
We can't repair what we broke
But I held you close, too close
I should've left your roses at the door
They're sharper than before
And I don't want them no more
Referencing back to the line about how roses can hurt you, he should have known better to pick up (or trust) this rose because it ended up stinging him with its thorns. The Rose most likely symbolizes his ex-wife, Kelis, who cheated on him, which led to their divorce.
There is no way he will ever be able to forgive or trust her again.
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