If your bf will not accept "something is wrong" with his child, there are no magic words to help make him accept it. 

You have 2 choices - 1. Change the way you feel about this and become "ok" with the child's unruly behavior or 2. Leave the relationship. 

I am sorry, but "love" is simply not enough to sustain a relationship. 

Say that you're worried about his safety. The running outside on his own thing can be dangerous. 

What if there is no such thing as ADHD? What if there is an underlying issue that is presenting itself as the symptoms of ADHD? My stepson was diagnosed with ADHD, ODD, and waking seizures. What I believe strongly is at the root of it all is serious trauma from when he was two when his mom allowed him to be abused by her boyfriend at the time. My partner worked so much he failed to miss the signs until the damage was already done. Long story short though, the trauma of both mom and kiddo need to be healed. If the trauma can be healed, and stronger constent parenting approaches taught to everyone, this child will likely be okay. 

What if your step son has an underlying issue? When his parents split up, were they able to be consistent around parenting between the homes or was there chaos? Does the child feel hurt by the split up possibly? Is he potentially bored in school and actually way smarter than he is given credit for? Is he dealing with something emotionally that he doesn't know how to put to words? 

There are a lot of reasons why children "present" the symptomology of ADHD. It's usually complex and there are multiple items at the core of it. 

I actually hate my step son's ADHD diagnosis. I hate all of his diagnosis because it gives his mom an excuse to continue to be a garbage parent rather than get the skills she needs and that both her children deserve and blame these "disorders" rather than her unwillingness to heal her trauma and work to heal her son's trauma which she caused. 

Everyone's story is different. I hope you guys can pull together for the kiddo. It's hard. 

Does your DH seem concerned at all about the behavior? Does he try to correct it with teaching, or routines, or discipline?

It sounds like either your DH truly thinks this behavior is ok (it isn't, who wants to live with all that?), or, he doesn't feel like dealing with it and is just throwing his hands up or putting his head in the sand. It's probably easier for him to tune out the behavior like running around screaming and making noises than it is for you to, since it's his biological child. It sounds miserable for you, and it's going to cause SS problems in school and in life if he doesn't learn how to act.

Some parents don't believe in medicating kids for ADHD, but something has to be done about it or SS will not be able to function in the world with any success. And for you, that means he won't launch. He would do well with a routine, and with clear rules with clear, consistent consequences for bad behavior and rewards for good behavior. Meds help, too, but denying the problem and doing nothing is probably easiest. For your DH, anyway, for now. 

‘he’s just an 8 year old boy.’ 

"Then why aren't you parenting him so that he behaves like a normal 8 year old boy?"

There is no way his restaurant behaviour is typical of an 8 yo ... nor of a 3 yo if the parents are doing their job right! But I know you know that - why can't he see that? 

For the running out of the door, either put a dead bolt or a chain at the top of the door so that he can't open it and throw it wide.

I have been a teacher for almost 10 years and SD was diagnosed with ADHD and anxiety shortly after I met her. At the time, DH was too "chicken" to discuss with BM. She is anti-medicine and doesn't believe ADHD exists. She said any issues SD was having was because "she needed her mother most." Yeah... so that conversation went no where for about 3 years. ADHD presents itself different in girls though. SD is more absent minded, can't finish a task, unorganized, and impulsive. 

With DH, I opened the conversation with "If ______ could do xyz, it would help her so much!" As she got older SD became VERY self-aware of how things were different and difficult for her. She became extremely self-concious and has VERY low self esteem. We took baby steps. We did counseling (her LCSW said she needed meds) and educational testing over the course of a couple of years. Fast forward to 200 - FIVE years later, SD is failing 5th grade and BM FINALLY said, "Well, I guess medication wouldn't hurt to try." THANK YOU. BM has finally come around the corner and SD is getting the help she has desperately needed for SO long! Get your SK help while he is still young, please. 

Perhaps the child's teacher could have a word with DH.

My sis tried to encourage her daughter to get her son tested. She just got mad, said she was being ridiculous. She home schooled the kid for years so never was forced to have him tested by the school. By the time he was diagnosed they had wasted a lot of years of treatment that could have really helped him be more successful. Parental delusion can be strong

His teachers have to see it 

Unless this is just bullshit manipulation of daddeeee for the kid to get away with incessent crap.

Or, just be direct. Tell DH that he has repeately dodged the topic of behavioral testing for the Skid and it has to happen now as he is losing developmental ground every day it is delayed.  Point out the behavioral crap he perpetrates incessently at home.  Start ordering books on the topic and leave them on DH's side of the bed, start asking other adults about normal and usual behaviors for 8yo boys and children in general. While DH is in ear shot.

If you do not push it, nothing will happen any time soon and it may be far past the time where intervention could help this kid.

I would say from what you describe... this behavior is far from 'normal'.

If the kid's parents refuse to see it, there's absolutely nothing you can do. Do not allow yourself to care more than they do.

He's not your child. He IS your problem if you choose to continue living with him (and blind Daddee). Decide if this is something you can do for the next 10 or 15 years.

SS 34 (??) has high-functioning autism, AKA Asperger's Syndrome. I pointed this out one time--once only--to DH when the kid was about 12. I was rewarded with an icy denial that anything was wrong, and I was informed that I did not know what I was talking about. Um, OK. Once burned, twice shy. I haven't mentioned it since. SS has received no diagnosis or help of any kind. I decided I could live with the EOWend custody arrangement, but I could not have tolerated much more.

Twenty years on SS is well down the predictable Aspie path--he's smart but socially inept. He alternates between displaying the personality of a cinder block and being a mean little sh!t. He has a good job and income, but there's something off about his looks and even at his best his behavior is a little off kilter. Girls/women give him a wide berth. He is likely to remain single all his life and he is not progressing in his career. Meantime DH says nothing  but I think he's come to see that actually I did know what I was talking about. (Actually I suspect he's always known but prefers not to face the fact that something's not quite right with his son.) Over the years SS's behavior toward me has been atrocious and mostly unchecked by Daddee. As a result I have come to detest SS. Even so, I'm sad that he never got help and proud of myself because I've managed not to say "told ya so!"

Please do not have children with this man. Neurological abnormalities such as ADD (and autism, which it sounds like this may be) are heritable and can be passed from parent to child. You have enough problems with one neurodiverse kid in your household. The last thing you need is to add a second one.

You're not on an easy path. I'd get out.