Why huh?

I still cannot understand why an 18 year old person could be so ungrateful to another person (who has spent numerous hours to provide FREE tuition/help) . Yes, I'm that 'volunteer' tutor (out of goodwill)... not those through VWOs. I had promised to help him until his 'O' levels are over and I've kept my promise. However when I broke news to him that I'm unable to continue helping him further due to my work and personal commitments, he spewed vulgarities and commented that I am selfish. Hmm... SELFISH? Well... well... Surprisingly, I'm not angry (not sure why)... just a little sad. Sad because I cannot convinced him that he should be appreciative of all the help (not only mine fyi) that he has received thus far, and that his "everyone owes him a living" kind of mentality is just not right.

Not sure if anyone out there understand how I feel.