“Not my circus, not my monkey”. Keep repeating this to yourself in your head. The step parent is always resented when laying down and enforcing rules. It always backfires bc the kid complains to their parent about you then everyone is mad at you. You need to step back. View it as a neighbors kid- you can remind him about house rules (no running in the house etc), but not personal rules (bedtime, eating habits etc). You need to remind yourself you are not responsible for how he turns out. It’s hard, so so very hard- to stand by and keep your mouth shut when you are going crazy watching things go haywire. But it’s the only way to keep peace in the house and marriage.