Here's what happens:
* Hamlet's behavior changes: Hamlet, distraught over his father's death and his mother's hasty marriage, becomes distant and erratic. Ophelia perceives this as a rejection of her love.
* The "get thee to a nunnery" scene: This famous scene is often interpreted as Hamlet rejecting Ophelia. However, it's more complex than that. Hamlet is deeply disturbed and driven by his desire for revenge. He expresses doubt about the nature of love and the world in general, leading Ophelia to believe he no longer loves her.
* Hamlet's feigned madness: Hamlet's erratic behavior is partly a facade to throw off suspicion about his plans for revenge. This makes it difficult for Ophelia to understand his true feelings.
* Hamlet's ambiguity: Hamlet never explicitly says he doesn't love Ophelia. His words are often ambiguous and open to interpretation. This contributes to the tragic nature of their relationship.
In essence, the tragedy lies in the fact that Hamlet never reveals his true feelings to Ophelia, leaving her heartbroken and ultimately contributing to her descent into madness.