Very good question! When thinking about Romeo and his infatuation with Rosalind, it is important to consider Act II scene 4, when Romeo tells the Friar about his new-found love for Juliet and how it has superseded his former love for Juliet. What is interesting is how the Friar talks about his former relationship with Rosalind. Note how the Friar says to Romeo that he had chided him for "doting, not for loving, pupil mine," which suggests that from the Friar's perspective at least Romeo was completely infatuated rather than in love with Rosalind. Also let us consider what Romeo himself says about his love for Juliet, and how he implicitly compares his love for her with his love for Rosalind. Somewhat exasperatedly he says to the Friar:
I pray thee chide me not. Her I love now
Doth grace for grace and love for love allow.
The other did not so.
Although therefore he does recognise that his affections have changed rather swiftly, at least he himself identifies the difference with his relationship with Juliet. This relationship is one of equals, where grace matches grace and love is wedded with love. He is able to state categorically that his relationship with Rosalind, perhaps supporting what the Friar said, did not allow for such a marriage of true minds.