In Shakespeare's Romeo and Juliet, the two young people start out as lovers and soon secretly marry. If I understand your question correctly, you are asking about the other roles each takes on because of the other.
This seems to apply to Juliet (in my mind) more than Romeo. For instance, with Romeo avenges Mercutio's death by killing his murderer, Tybalt, Juliet casts him in the role of murderer himself, even if only for a short time. Her disbelief in what he has done soon gives way to anger, resentment, and perhaps even hatred in that he has killed her cousin. Her response is understandable to a point, but also naive; for this is the relationship that exists between the Capulets and the Montagues. And while they try to overcome the hatred that exists between their families, it is unrealistic to believe they can love each other, marry and remain unscathed.
O serpent heart, hid with a flow'ring face!
Did ever dragon keep so fair a cave?
Beautiful tyrant! fiend angelical!
Dove-feather'd raven! wolvish-ravening lamb!
Despised substance of divinest show!
Just opposite to what thou justly seem'st—
A damned saint, an honourable villain!
O nature, what hadst thou to do in hell
When thou didst bower the spirit of a fiend
In mortal paradise of such sweet flesh? (III.ii.76-85)
Juliet resents that nature made Romeo look so sweet when inside—contrary to his beautiful appearance—lies the heart of a "serpent," "a wolf-ravishing lamb," a "villain," and a "damned saint." Here Juliet casts Romeo into the role of criminal, betrayer and murderer. This is her initial response.
Finding a role that Romeo thrusts upon Juliet is more difficult. One that I find that seems in keeping with the times (but not with Juliet's personality) is the role of a "dyed in the wool" Capulet and a weak woman. When he kills Tybalt, Romeo is despondent—even suicidal. He believes that he has destroyed his relationship with Juliet by killing her kin. He believes her blood connection with Tybalt is stronger than her love for him. He has no confidence that she can get past what he could not stop himself from doing. When he goes to see Friar Lawrence, he believes his life is over. When the Nurse arrives, he asks:
...How is it with [Juliet]?
Doth not she think me an old murderer,
Now I have stain'd the childhood of our joy
With blood remov'd but little from her own?
Where is she? and how doth she? and what says
My conceal'd lady to our cancell'd love? (III.iii.97-102)
When Romeo bewails his banishment from Verona (though he deserved to be executed for breaking Prince Escalus' laws about fighting), he never stops to think that Juliet has the capacity to love him enough to follow him. She has already defied her family's wishes by secretly marrying him: she will ultimately fake her own death as well. Romeo casts Juliet into the role of a weak, grudge-carrying and only partially committed wife. Had he had a clearer understanding of who she was as a person and as his wife (based on her devotion to him), the play might not have ended so tragically.