Hi, im no expert as my husbands kids are grown and out of the house and I myself do not have kids...but I can tell you if you dont make a change now, IT WILL NEVER END!!! Have you spoken to your boyfriend about how his son acts? Does he discipline him at all? Sounds like the son is acting out either for attention, rebellion other reasons as you mentioned (about the mom or maybe he is angry about living with you and your child?). All I know is fix the problem now because it will only get worse. My husbands 19yo daughter started having MAJOR issues about a month after we got married and now Im SCREWED. She doesnt even live with us and she is ruining my life and what was supposed to be a year of newlywed bliss!!!!! For now - when you get angry with him either walk away or keep telling yourself over and over that he doesnt know any better. These are likely his toddler coping skills. 3 is young to take to counseling but maybe you and your husband could talk to someone about parenting him together since you are mostly the one home with him. There has to be some way to cope without losing the person you love over a kid. If you find the answer let me know!