It doesn't work and I don't understand why my dad became abusive...

I feel like therapy doesn't do jack shit.....I have been going since I was a teen and nothing has changed....Instead things have just gotten worse...I'm thinking about stopping therapy all together now ...I also had a question...Did anyone else have a loving parent until a step parent joined the picture then they both started to abuse you...Because that's what happened to me...I don't understand why it happened...