Questions & Answers about Arkadaşım üzülünce ona çay veriyorum.
Because arkadaşım means my friend.
- arkadaş = friend
- -ım = my
So this is a possessive ending, not a case ending. The subject of the sentence is arkadaşım = my friend.
Üzülünce comes from:
- üzülmek = to get sad, to be upset
- -ınca / -ince / -unca / -ünce = when, once, upon
So:
- üzül-ünce = when he/she gets sad / when my friend gets sad
The suffix changes form because of vowel harmony. Since üzülmek has the vowel ü, the suffix appears here as -ünce.