[Adam the Fish]

Hey, welcome to TeenHelp!

To be honest, I'm not sure what changed with your dad.
It might be because you've got a boyfriend, or possibly because of the side-effects of that (your improvement mentally) meaning that not only is he less stressed, but you're probably easier to communicate with and see things that he says in a more positive light than he used to.
What he said about how things would be your fault was untrue, misinformed and not very good, but giving him the benefit of the doubt, I'd say that he wanted to help, but didn't know how...and so tried shock, a method that is probably not really advisable.

Of course, it might be something else completely anyway!

So...yeah, possibly it's not a good moral reason that he has changed, but I'd try believing the best of him. I prefer to believe the best of people.
Give him the benefit of the doubt and be glad that he's better now .