This is indeed Depression.

Why he keep pushing himself to be perfect?

And why his group mates buat tak tahu?

But he mentioned about forgetting past.

I think he have concussion or something that made him lost part of the memories.

Yes, it is proven here "Teacher, is this what you wanted to hear?"

Maybe his teacher pushing him hard due to company's objective too. And while other group members are doing good compare to him...he stressed out kot.

yeah. Depression is dangerous.

I once had minor one. but luckily not that serious, still able to live happily back to normal.