I want to spit in his drinks
Why do you want to spit in his drinks?
He's a fat pig and I hope that it will make his heart stop working
Spitting in someone's food doesn't just open you up to battery charges, it can also result in food tampering charges if the victim contracts an illness. If you have an issue with your boyfriend, you should sit down and talk to him rather than jut trying to get back at him.
Don't worry I will do it slowly. He will experience no sickness or visible changes in behaviour at first.
You are better off ending the relationship.   There is no need to end things by committing a crime.