I am so sorry you are going through this. Trust your gut, protect your infant, and find the dog a new home (either temporary or permanent) until the situation with Sal can be resolved. You don't want the dog to be hurt or worse by your stepson.
From what you describe, Sal is not safe in your home and with more vulnerable individuals (human or pet). If it were me, I would call the therapist and make sure they understand the gravity of the situation. What he has done with the dog may be a crime, I would investigate whether or not he can receive additional therapy/services due to the fact that he has committed what might be a sexual offense.
Almost as much as the situation with Sal itself, I am concerned that your husband seems to either be in denial or in so much shock that he cannot take action to protect his other child, you, and your pet. Acting like none of this ever happened is the worst possible thing that can be done, and will ensure that NOT ONLY will it happen again, it will probably get worse.
Trust your gut!
