It's difficult cause I think he was upset about all of them

He completely lost it when Sirius died.

ok i know this a hard qn, especially between black and dumbledore but i think that it was harder on harry as dumblerdore though not related was like a father to him. harry greatly respected him and dumbledore always looked out for him. i know Sirius black did too and is his only family left but some how dumbledore's relationship with harry seemed much closer

It was the first person that was very close to him who died. And, out of all three, Sirius was probably the closest person to him.

i'd say Dumbledore's. He was like a God to Harry.

This was hard to cuese but i think Harry did most love Sirius but Dumbledore and Dobby aswell..

dobby comes next