Talk to your Mom about your concerns- let her take the lead. Invading your step dad's privacy (even if it is for a good reason) could be truely devastating to everyone concerned, no matter the outcome. You seem well intentioned but what you are wanting to do will only lead to heartache for everyone including you. If there is a danger of abuse because of this go to your school counselor- they are required by law to protect you. I'm sorry that you are going thru this.