Your running use of the herbal metaphor works well. Especially I like your use of the symbolic meaning of the herbs to expand the content of your poem. Blank verse works well here. You liken yourself to a fragile plant, no hard wood grows on these herbaceous plants. You are wrestling with the question not of blame but causation. Did you sabotage the relationship or were you betrayed? You come to the conclusion that both you and the other are the “root” of the trouble. Within yourself you find no grounding (Rosemary = remembrance) of courage (thyme), while developing only false love (stale baby’s breath). On the other hand the other undermined your self confidence and confined you. When they left, you found the space to grow you had not realized you needed.
this poem is chilling and sad in equal measures. Overall, the self berating message of a missed opportunity, allowing a treasure go to waste is effective and resonates. That punchline though is powerful - superb throughout!