My confusing friend

Hi guys.  I wanna share something about my friend.

Okay, let's call him Dep.  

Dep used to be a funny, hilarious and happy boy.  But this year, he had completely changed into a different person.  He's very depressed and he cut himself.  I don't know why he sometimes acts like he was very happy and laughed like there was no tomorrow!

Sometimes, I will think that he's lack of attention a.k.a. LOA.  He chooses those popular people over me and my friend.  And they treat him like he was just a normal friend.

Yesterday, Dep was crying.  Jin (my friend)and I skipped our class to comfort him.  Before we left the class, we asked Dep's so-called friend to come too, and he said no cause he's studying.  So much for being a friend.  I told Dep that and he said that his so-called friend patted him on the back.  Seriously, patted him on his back! I'm usually not that mean, but it's just not right that you're best friend is crying there and you just sit there and stay calm.

I hope you guys can at least tell me how to stop Dep from cutting himself...  Thanks anyway