Comparative study of the romance between Rosalind and Orlando and of Touchstone and Audrey?
This is a thougtful question, Icshakti, and one that gives a good insight into the question, "What is love?" as a main theme in As You Like It.
To begin, the question was a very real one for Shakespeare, since he was writing at the very end of the Renaissance, and the ideas of courtly love and marriage by contract (rather than our modern Western idea of marriage for love) were changing. So, the question of love and what that has to do with marriage was a real, evolving concept for people in Shakesperae's day.
Shakespeare examined all "types" of love in his comedies. In As You Like It, both Rosiland and Orlando are high born people. They fall in love at first sight, but in their very ordered world at court, might never marry unless such a relationship was contracted for them. Definitely Rosiland would never be permitted to be the "leader" or "suitor" in the relationship.
When they go to the forest, she, dressed as a boy, is able to leave all that courtly convention behind and pursue her love. They still follow all the courtly procedures of high born love, though -- speaking in verse to each other, writing love notes, etc. It should also be noted here that their courting is not direct (even though they are no longer at court), since Rolisand is dressed as a boy and teaching Orlando how to be a good wooer of his lady love. Their relationship and how it turns out is central to the plot of the play, so the audience is meant in invest a great deal in whether they end up together or not.
For Touchstone and Audrey, the most important distinction is that they are low born characters, which means that, within their function in the play, they speak in simple prose (sometimes using bawdy language) and are meant to serve as comic relief. Another difference is that, since the plot of the play does not revolve around their story as it does with Rosiland and Orlando, there is no serious plot question hanging on whether they end up together or not.