Your husband needs to respect that and stop making everything about skids. Its not just skids and he needs to stop over compensating

when i gave birth my ss was 17.5 and 19 when both our kids were born. When it was time to go to hospital, ss was told we were going to hospital. Nothing else was more important. My husband also made sure after i gave birth that ss didn't go to hospital because he'd quickly get bored and wanna go home and hubby wanted to spend time together.

the most issue we had with exwife was her trying to make me drop everything for sd's when i had a 1 & 2.5 yr old like her daughters were centre of the universe. I stopped this nonsense pretty early on because it was biomum trying to meddle in our household somewhat.

my son has allergies to egg and cats and sd's have cats at home and were covered in cat hair everytime we met and my son has an epipen so we do control who he is around because he gets very sick very quickly and i make no apologies for being a mama bear in that respects.

how your husband is behaving isn't normal and its him still being rooted in his previous family as his world. The times have changed, he has a new family and although his exwife is the mother to 2 of his kids, she is not your family or his family anymore

your husband/partner needs to recognise and accept that and make sure his kids understand that too. My husband's exwifes family are nuts and into black magic, i made it clear to my husband that his daughters don't get to take pics of our kids and show them/send them to bio mum and her family because of the harm they could do. Her dad and brother had years ago during the divorce threatened to stab and shoot my husband to death so my husband has accepted and of his own accord ensured that bio mum or her family never be near us. 
 

unfortunately communication is key but even more difficult when your husband is getting angry and somewhat violent with you because he refuses to hash things out as an adult and see where you are coming from.

end of the day, your health and that of your preemie baby comes first. If you do not want biomum to have a pic of your kid because its not her family then you have a right to that being respected and not hubby making this about ss. Your kid is a minor and didn't consent to exwife having his pic. 
 

there are only 2 people who get to dictate access of your kid (you and your husband) but when one of you feels uncomfortable and is against ex-family or extended people having pics or access, then your spouses views should be respected as a priority

OK, from the top ...

"The entire pregnancy was spent talking about how he would never forget his first two especially his son.

What is the matter with him? Doesn't he know that love isn't finite and that you can love another child without depriving the others?

"anything you say that’s what he says “that’s my son”.

He has an unhealthy attachment (obsession) to his son. Why is that? Why doesn't he seem to have the same feelings for his daughter?

"Fast forward to giving birth one week post partum he’s yelling at me because I’m in the bedroom with the baby locked up and I don’t want the kids in the bedroom."

This is the point at which I would have packed and left with my baby. You need time and space to bond - even more so if you're trying to breastfeed. And I agree with you that the adults' bedroom should be child-free as a rule. Everyone needs a safe space and your bedroom should be your sanctuary. Does he know nothing about childbirth? Where was he when his first two were born? He actually sounds as if he resents your child - did you discuss having a child together before marriage? 

"if we’re having a conversation they jump in."

Does he actually parent them at all or does he let them do what they like with no rules nor boundaries?

"Now it’s his sons bday and he’s hosting it with her."

So he says one thing to mollify you and then goes back on his word. Why is he so keen to keep his ex happy? You can be cordial with an ex without playing happy families. I wonder what her husband thinks of having the guy who used to sleep with his wife around so much?

"But DH is on her side with it all and yelling that that is his son and he will give him what he wants."

So what YOU want is of no consequence? All I can suggest is counselling and if he won't go then you'll know that your marriage is more important to you than it is to him and that there's no point in struggling with someone who has so little regard for you. He apparently has forgotten his vows - isn't there a bit about "forsaking all others"? 

I asked him to let me go then because this is not the life I want. Am I wrong?

The problem isn't BM, it's your husband 100%. There would be no problem with her if he set boundaries and respected you, his new wife rather than pandering to his ex. He doesn't seem to be able to say no to her nor to his kids but has no trouble yelling at you. 

You are not wrong for not wanting this kind of life. If you don't want to live like this then don't but make sure you have a pit-bull of a lawyer for your divorce and make no concessions (i.e. don't sell yourself or your son short in order to be Ms NiceGuy).

Start by not going to this party. Not your child, not your problem. Have a nice quiet day with your baby. As from now, put your foot down about what you will and will not put up with. 

Tell him that you didn't marry him to be a sister-wife to his ex...

Some people want those social media exes that are still just a big happy extended family- but if that was the case why did the couple break up?

Sure there are events that will be joint in the skids lives. School functions, sports, etc- those are things that all parents wind up doing together. Birthday's, holiday's- no. Those can be done separately. 

Your husband really needs to stop and figure out where is priorities are. Have you tried marriage counseling? Someone who has REAL experience with this kind of stuff and isn't going to tell you to suck it up "for the kids"? 

You aren't wrong for having boundaries with your husband's ex. The real concern to me is why he doesn't. I do think that there is a possibility for your relationship to be saved but in this case he is going to have to make some big changes to make your marriage the priority. 

This would be my hill to die on. There is no reason to be buddy buddy with an ex. They are an ex for a reason. You can still 100% co-parent without having joint celebrations and be all up in each other's families. 

Since your DH fails to have the balls to put boundaries in place, that will have to be yours to do. I recommend taking your baby and leaving before the birthday party. Just a Mommy/Baby day and returning after all the festivities are over. That way, you don't have to play fake nice with BM or worry about your baby being in the middle of the circus. If DH gets pissed, oh well, he couldn't honor your boundaries. I also second therapy. 

So he has a son and a daughter already, and your baby is a boy. He keeps repeating "That's my son!", and now is going back on his word to you by doing things with BM and even wants yo involve YOUR son with BM? This guy has some deep-seated issues. Maybe he is upset because SS has been "dethroned" as his only son? I'm hearing "HE's my son (points to SS), not him!" Could BM be putting these "poor SS" ideas into his head? I recommend therapy since you have a baby with DH, and it's too soon to give up. BUT - what's going on now is not ok. It's not fair to you or to your baby. ETA i think if you had a daughter, then SD might be the focus of DH's obsession and anxiety. 

And take "his son" and any other failed family spawn with him.

it's not so much his ex as it is your dh never set boundaries with her.  she is thinking "blended family".. you want separate family.

I can see wanting a picture with all the siblings. which they are all siblings..even if the yuongest two are not sharing genes with each other.. they both do with the Skids.

but.. your dh went back on his promise to not do the joint events.. and in hindsight... seeing that in practice before you had a child would have been better timing... so at this point.. either he starts valuing your boundaries.. or he may have another EX on his hands.

When DH and I started dating I was open to being friendly with BM. Until she made it very clear she is psycho.

I guess your DH hasn't noticed the passive aggressive jabs your BM makes. If that's what they are. It's possible she's just really stupid.