Honestly, rather than making this an issue of piety-which turns most of us off-just be a solid friend. That means don't enable or clean up his messes, don't preach or judge but most importantly, support him in endeavors that are ethically based-self improvement, care for fam, introspection. Most people go through their paces or pass through stages and come out alright.
We as a community need to be waaaay less judgemental-it's disrespectful to all involved.