I am sorry for what brings you here. The pain of loving an alcoholic/addict can be devastating. I've gone through the heartache of having someone I love tell me they no longer love me.
Sometimes there are no answers to why.
You won't realize it now, probably not for months or even years. But you just had an abusive, pot smoking alcoholic with paranoid personality disorder break up with you.
You will thank your lucky stars one day.