Instead of teaching about equality. 

Everyone is not equal in our home, but we make sure that there is equity in our home.  Equality means that everyone gets the same, while equity means that everyone gets what they need.  It was easy to explain to the kids when they were little.  I used a shoe analogy: I wear a women's size 10.  If we practiced equality, everyone would get the same women's size 10 shoes, which would work great for me, but terribly for anyone else.  Under an equity model, everyone gets the size shoes that they need.

We're also really honest about the differences between the kids...  DD15 is a college-bound overachiever who is with us 100% of the time, where SS16 is headed toward vocational school and here 70% of the time.  Both are A-OK in our book, and reflect the interests of the kids.  There is no competition between them, but it means they need--and get--different things and different support from us.

Tell him he's right, you can't stand his son, because he's poorly parented and doesn't listen. Don't let him make you defensive about bringing up the subject. 

Here's a primer:

https://www.steptogether.org/help.html

Your bio and SS will be treated differently by you. Good parents don't let their child do whatever they want. They parent. You will parent your child.

It's not that SS does not grasp anything. It's that his dad is letting him do whatever he wants. He is giving you less authority than the babysitter he would hire by the hour. If the child repeatedly sat on the balcony rail after being told not to, the babysitter is not going to return. No reasonable person wants to be in charge when the child falls off. Dad will not back you up and SS knows that. SS knows that Dad doesn't respect you, so he doesn't respect you.

You have a BF problem. BF is letting his son do whatever he wants while BF plays video games. 

Since you have a child with BF you have some hard choices. You can't just walk away and never look back. You might try counseling for you to help you decide what to do.

About loving your bf child like your own.

 do you believe that you MUST love a non biological child like your own bio child?

It's hog wash.

If anyone tells you that again---ask them if they LOVE the neighborhood kid up the street like their own kid? Or what about the kids in your kids school? Do they loveeee the school friends just like they love their own bio kid?

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My DH is the same with his son, Nothing SS does is wrong. My husband had to climb up onto the roof of our house becasue we had a leak, he had left a 6 ft ladder set up going from the ground to the deck and then a 30 ft going from the deck to the roof. I was standing at the bottom where the 6ft ladder was. SS kept climbing on it and I must have told him 10 times to get off and stop he eventually just kept ip up until he had climbed the ladder to the deck and then climbed over the deck fencing. I was furious and said I'm telling your father. What a mistake that was,DH all but congratulated his son for doing it. I said you have to be kidding me, I told him NOT to do it. I said to DH that in the future I would be sure and just let SS do whatever it is he wants to do regardless of how dangerous it could be. I was told he didn't get hurt so whats the big deal. OK I'll remember that. My DS is 21 a young adult, he still lives with us becasue he can't afford to move out on his own (we aren't forcing him to) he helps out with household bills. DH treats my DS very differently than his own, the age difference has nothing to do with it. DH thinks my son is strange becase he has OCD and washes his hands a lot well and his son has to be told to wash his but that is fine. His son is lazy and a slob, leaves food and crumbs all over his room, My son doesn't like to eat or drink in his room and to DH that is strange. I stopped commenting on SS becasue it is useless and when DH has a comment about my DS i just say that is your opinion and you are entitled to have one, doesn't mean you are right. 

Your child is 9 months.. his is 7... of course they aren't being treated the same.  people won't have the same expectations from an infant vs an older child.  Also.. yes.. the baby IS your child.. his is not.  He should be the one to parent his own child.. and if you can't be involved in that because you can't do it from a position of "caring" (not love.. but at least care".. then it is best that you aren't charged with taking care of him anyway.  

I mean.. the kid is 7.  He is not a fully formed person at that stage.. some kids are better behaved.. but lots of kids have to be told the same thing over and over... slow learners so to speak.  I'm sure the child isn't intending to get on your last nerve, but with a baby as well.. I'm sure you have plenty on your plate.

The thing is... your child will be raised the way that you want to raise him.  In the end, raising a child to be more well behaved is actually a benefit.  So.. if the kids are not being parented "the same"... the way you think you will parent your own child should statistically make him more successful...so different isn't always a bad thing.

I don't have the same issue as you but wanted to respond because your post made me think of my own problems. I'm embarrassed to say that DH makes comparisons to our DS5 and SS16. Yes, he compares his 16 year old to our 5 year old. Plus, he calls out (yells, in fact) our 5 year old for things but says nothing to SS16 for doing something similar. It's infuriating to me. Makes me want to divorce him, but I don't want my kids alone with him and SS. I need to oversee my little ones.
I am disengaged, so I don't say much to SS at all. It's all about parenting and being honest with your kid. I can tell my 5 year old that he isn't being/playing nice. I can tell him he needs to apologize. I can explain to him the consequences of his actions. But I don't do that for SS. DH isn't honest with SS, doesn't call him out, and doesn't parent him due to whatever guilt he feels. BM is the same.
DH keeps saying that SS has the mentality of an 8 year old, so he treats him as such. Nope...I don't buy it. He's a junior in high school and has the privileges of one so should have the responsibilities of one. It seriously pisses me off when DS is held to a higher standard than a near adult.