I'm ruining someone's life.
Is that something you want to do?
Yes, I hate this person immensely.
I think deliberately trying to ruin someone's life is going too far. Your letting your hatred for someone really impact you. You should leave them alone.
I'm going to ruin his life.
You should focus on yourself instead of spending so much energy trying to ruin someone's life. In the end, it's not going to benefit you in any way and will most likely cause you harm.