Barbara makes an excellent point, what would your motives be in telling his parents? What would be gained by that? Codies and helpfulness tend to lead to bad choices.
Keep reminding yourself you are an EX and need to focus on you not him and his issues. And wanting to reach out to his parents doesn’t go with EX status. You love him, his parents love him but none of you can love him sober.
Keep posting and talking with your friends, reading and looking out for you.