Step Son Vs Bio Son

Backstory: my husband and I were together a few months before he found out he was going to be a dad from a previous “encounter”. We moved in together end got married shortly after that. So I’ve been SS’s step mom from birth. Fast forward 5 years and I now have a son of my own (1yo) and SS has started acting out which we expected but we are getting zero help from his mom with his behavior. Now I constantly find myself being annoyed by SS because his behavior is exhausting. I grew up with an older step sibling and I never want the issues we had (resentment, etc) to come between the boys. I’m frustrated with these feelings but I feel like I have zero help other than my husband.