8yr old sibling abuse

Hello, I have two boys soon to be 7 and 4. My boyfriend has custody of his ex girlfriends son who is not his biologically but is treated like his son nontheless. My boyfriends son has ADHD .  Anyways about a year after living together my boyfriend's son Jason decided to have my children touch each others private areas while he watched. They were talked to and Jason was told that this behavior was unacceptable and disciplined by not allowing certain priviledges tv, nintendo etc.  Anyways, after this incident Jason has had several incidents in bath tub where I caught him trying to kiss my boys or touch their butts the minute I would walk out of room. So i didn't allow bathes together any longer.  My boyfriend and I constantly argue about his son Jason's behavior because he is always causing chaos.  He has to be repremanded at least twice a day for lieing or fighting with my boys in an unsusual way (such as slapping or kicking on "accident") I don't know what to do? Then the other day he was caught asking my 3year to take down his pants so he could touch his private area (penis) and before that ran his hand over my 7yr olds private area but luckily he was under blanket and then I guess began spanking a stuffed animal's butt in front of them laughing.  I feel responsible that I looked at it so lightly the first time as "normal explorative behavior."  Jason has since been removed from the house to my boyfriend's mothers (jason is really close with her) and sh took him to he pediatrician who said the touching is normal.  I wanted to scream so now I am doing my own research because I think that it is my obligation as a parent to protect my children from this kind of sibling abuse. However, it has caused a lot of sadness becuase I told my boyfriend I was going to move out if Jason came back because I couldn't handle him or knew how to deal with this yet..please help?

[Kevin Kennedy, Ph.D.]

Well, I can't help you with whatever decision you make about staying with your friend. However, the sexual behavior is absolutely not normal. He shows significant lack of impulse control and, unsupervised, will very likely continue to dispay sexualized behavior and other impulsive acts. He requires professional intervention and I hope whomover holds custody of him arranges for this to occur.