He never seemed to feel bad for the pain he caused me.
people deal with stuff differently. or in the case of addicts, they try to NOT deal with stuff as much as humanly possible. that means tricky stuff like feelings, or actions. for if one were to stop and truly assess their current situation and all the wreckage they had caused, the lives they'd mowed thru, the people they had used along the say, if they truly thought about how much they had hurt their MOM or DAD or sister, TRULY with sober clarity, it would be too much, too overwhelming.
so what does the self respecting addict do? get loaded. get numb. add it to the Forget pile.
also as Zoso said - some people are amoral jerks without the drugs. many sociopaths are also substance abusers - addiction in and of itself does not CREATE sociopaths, but it can certainly MIMIC that behavior. when the drugs are in charge, all else is secondary.