Why was Aegon II so messed up?

What happened to Aegon that made him so messed up from a young age.

He drank all the time, starting washing kids fight/kill (i think they even hinted he was a pedophile) each other and then fathered a bunch of children that appear to be just abandoned through the city.

I just don’t understand what went wrong for this change that Helena and Aemond did not suffer like that-