I am sorry that you are in a difficult situation. He is going to have to learn to trust you and he needs to understand that nothing more happened than it did.

Unless he is a doctor or pharmacist or nurse he would not have access to 'truth serum'. Even if he did that is not a good idea because the drug (sodium pentothal) is very powerful sedative and it sometimes is used for lethal injections/euthanasia. I don't think you want to go that route.