I am very sorry you are experiencing this and glad you have written us here.
This is tough because in many ways this situation forces you to keep a secret. This is not a good feeling for anyone. One reason it is so difficult is because you don’t have any real power in this situation. At 16 you are feeling somehow responsible for fixing this, but this isn’t yours to correct. Feeling responsible without being able to change things can be overwhelming.
I would highly recommend you talk to your school’s guidance counselor about your feelings. If you don’t want to talk about the specifics you can simply tell the counselor that you learned something about your parents that has caused a great deal of stress. The counselor can then help you find a therapist you can talk to. Right now being able to sort this through with someone who isn’t a friend or family member is the important thing to do. You need support from another source other than your mom and dad.