The relationship between Hamlet and Laertes, at least at the beginning of the play, is virtually nonexistent. We never really see the two interact, and when Laertes speaks to his sister, Ophelia, about her relationship with Hamlet, Laertes seems really to only talk about him as the future monarch of Denmark and not as a young man. Laertes says:
His greatness weighed, his will is not his own.
For he himself is subject to his birth.
He may not, as unvalued persons do,
Carve for himself, for on his choice depends
The safety and the health of this whole state. (1.3.17-21)
If Laertes really knew Hamlet well, he might be able to speak about him in more specific and personal ways; however, it is evident that he really only knows Hamlet as the prince of Denmark and not as a friend.
By the end of the play, however, the relationship between Hamlet and Laertes is quite antagonistic. Hamlet insists that he loved Ophelia more than "forty thousand brothers" could do, and Laertes is enraged by the fact that Hamlet murdered his father, Polonius. When they engage in swordplay, Laertes tips his foil with poison so that if he even scratches the prince, Hamlet will die. Eventually, the two reconcile just prior to their deaths.