We get the first hint of this in Act 1 Scene 2 where Claudius gives Laertes permission go back to France. What’s important in the scene is the way the actors are positioned. Laertes and Hamlet must’ve grown up together in court. But Laertes is not in a corner having a quiet final beer with Hamlet. He keeps his distance. So it is what is not happening, rather than what is, that is significant in this scene. The two do not speak to each other and there are no farewells. Certainly not good friends.
Before he departs for France, Laertes gives Ophelia some advice about Hamlet. Clearly Laertes knows Hamlet is a bit of a pants man, but not with his sister. This is not going to be a Wills and Kate romance. Laertes quite rightly points out to Ophelia that Hamlet, as Prince, may have no choice in whom he marries. In a practical sense he suggests,
Then weigh what loss your honour may sustain,
If with too credent ear you list his songs,
Or lose your heart, or your chaste treasure open
To his unmaster’d importunity.
I iii 29 – 32
Put bluntly, no bonking with the Lord Hamlet.
This message is later reinforced by Polonius. It is to have disastrous consequences.
But when Laertes returns to Denmark to find that Hamlet has killed his father and that his sister has committed suicide as a result, his dislike of Hamlet escalates into homicidal rage. In such a state, he is no match for the wiles of a politician like Claudius.
He agrees that
that, with ease,
Or with a little shuffling, you may choose
A sword unbated, and in a pass of practise
Requite him for your father.
And suggests that
I’ll anoint my sword.
I bought an unction of a mountebank
that, if I gall him slightly,
It may be death.
IV vii 134 -141
Both Laertes and Ophelia are innocents caught up in a world they do not understand and which ultimately destroys them both. What Hamlet says of Rosencrantz and Guildenstern’s deaths in England:
Tis dangerous when the baser nature comes
Between the pass and fell incensed points
Of mighty opposites.
V ii 60 – 62
is as true for Laertes and Ophelia as it was for the ” wretched, rash, intruding fool”, their father.