Hassan is the most noble character in Khaled Hosseini's The Kite Runner, and it is true that his finest qualities eventually cause him the most pain and suffering. Hassan will do anything for Amir, and Amir takes advantage of it.
The most notable quality Hassan demonstrates throughout the novel is his unconditional love for Amir. Though he gets virtually nothing in return from Amir, Hassan loves him anyway. Though there are many small costs (in the form of lost dignity or embarrassment), there are at least three times when his unselfish love for Amir costs Hassan severe suffering.
The first, of course, is the incident with Assef. Hassan finds himself in the alley with the bully Assef because he is determined to get the blue kite for Amir. He knows that Amir is desperate for Baba's (his father's) approval, and winning the competition would do that, for a few moments, anyway. Hassan gets the blue kite as a reminder of the humiliating assault. For Amir, Hassan accepts this, and he suffers alone and in silence.
The second incident happens shortly afterwards and is a direct result of the earlier incident. Amir saw the assault and did nothing, and now he cannot live with his guilt at running away rather than helping Hassan. Amir plants money and a watch under Hassan's bed and then accuses Hassan of stealing them. No one wants to believe--no one does believe--it is true, but Baba asks the question anyway. They all know that Hassan will never lie (another of his good qualities), so when he says he stole Amir's things, Baba has no choice but to believe Hassan and sends him away. Hassan is forced to leave his home because Amir acted like a coward; if Hassan had not loved Amir so unconditionally, he would not have been sent away.
Finally, Hassan comes back to Kabul at a very dangerous time (especially for a Hazara) out of his love for and commitment to Amir and Baba. When Rahim Khan can no longer take care of the estate on his own, he finds Hassan, who is living in a remote village. If Hassan had stayed there rather than doing what he felt he must do for those he loved, Hassan would not have been killed by the Taliban.
For Hassan, love and suffering are often connected; despite that, he manages to maintain his love and his unselfish character. Putting this in a speech should not be too difficult. Choose any three incidents (the three I gave you or add anything else you can think of) which cause Hassan to suffer, and you will probably be able to trace them back to the fact that Hassan loved Amir more than he loved himself.
Keep in mind that Amir always blamed Hassan for everything he did, and Hassan let him do it, taking the consequences without complaining. This is the embodiment of Hassan's unconditional, unselfish love for Amir:
He stopped, turned. He cupped his hands around his mouth. ''For you a thousand times over!'' he said. Then he smiled his Hassan smile and disappeared around the corner.