First off, engaged men are FIANCE, engaged women are FIANCEE.  Sorry to be Ms. Grammar Nazi.

Secondly - I get being annoyed, but the extreme nature of your reaction seems really, really out of proportion. It's his FIRST birthday, not his medical school graduation.  He won't even care about anything except the boxes his gifts come in and screaming miserably because he needs a nap and he's stressed out by all the people and gifts.

DH has two children, and it will take time to settle around that for him. You may not care about SD as much as he does, but for him, this is a question of whether his first child will feel left out and he'll need to sort that out.

I think a first birthday party with no other kids will have more adult foods, Ones with toddlers may have different planning.  

Let it go.  

I read your other post.  I think you need to take some breaths and slow down.   Looking for pain in the littlest actions will only hurt you and your relationship.  

That seems extreme. I know it’s a moot point, but I don’t understand why someone who would react like this would choose to be part of a blended family. I also think that your love for your child has made your response disproportionate to the actual offense; so it should be easy for you to understand how his love for his other child makes him want to make sure that she’s included. Imagine if someone leaves your kid out of something once he’s old enough to understand. (To be clear I understand that you weren’t going to leave out SD, just that DH wanted to make sure she wouldn’t be.) Just think about how your love your child, and understand he feels that way about SD.

At this point you want to build a happy life with this guy, so you’re going to need to come to terms with the fact that while your focus is solely on one child, he has to balance two. I’m sure there are going to be bigger challenges ahead with shared resources/attention, so you’ll need to learn to let the little stuff go to make things work. Of course, there may be other situations where he is in the wrong, I just don’t think this is one of them.

Both kids should be focused on and paid attention to because they're KIDS, regardless of the day. But both parents need to emphasize that it's ONE particular kid's "special day" and it's about them. That doesn't mean ignoring or not included the older sibling, it just means older sibling should be reminded ahead of time that it's XYZ's birthday and they will be getting lots of attention, presents, etc. and there should be no jealous outbursts. It's the same regardless of whose birthday it is. It's the same on her birthday, right?

But you need to understand that these are BOTH of his children and it should be celebrated as a FAMILY event. SD should be included in the celebration of your little one. I get the feeling that SD makes everything about herself and DH goes along with it? If so, sit down and explain to her yourself that this is her brother's birthday and you're happy to celebrate as a family but you expect her to let the day be about him - just like her birthday is about her. 

My SD used to have jealous outburts, ask "why don't I get that?" when I bought BS things, etc. but eventually, before his "half birthday" (Yes, I celebrated his 6 months as a half-birthday - I made a cake and everything!) I sat her down and said enough is enough. You are part of this family and you are expected to act like it. No more outburts, no more attention hogging, none of it is acceptable anymore. Your brother can and will be the center of attention sometimes. Your brother can and will get toys/things you don't get. You are no longer allowed to throw fits or act up. You will be sent to your room when you do. 

I also explained to her that there will be plenty of times in life where SHE will be the center of attention and SHE will get things he doesn't get. This is the way it works in families. Unfortunately, the young baby/toddler years are filled with this simply because they are learning, growing, becoming little humans and there's a lot of little celebrations/new age-appropriate purchases that come along with that. I explained that one day, she will reach an age where there's lots of little celebrations/new age-appropriate purchases too. This happens a lot from middle-school onwards - graduating, first day of highschool, first time driving, etc. 

We all have phases in our lives where there is a lot of change and the family needs to experience and celebrate that change together. She needs to understand that she also had a first birthday, her first steps, her first time sitting on the potty, etc. and they were enjoyed and celebrated by everyone around her too. After I explained all this to my 7-year old stepdaughter, she really came around and started acting like part of the family. In fact, I'd say she started truly loving her brother and feeling more included. 

Would you feel differently if this was your second child with your boyfriend? What would you do then, hide child number 1 somewhere so you can just have a party for child number 2?

Here is an idea...get two cakes. Celebrate with your boyfriend, you and baby just the 3 of you first??? Is that possible?

THEN pull out cake number two and have a party?

That what I would do if I were in your shoes.

We just had my YDS 1st birthday and I was fully prepared for the event to somehow be made to be about SD because of how family members have acted in the past so I get where you are coming from. 

DH also used to insist that any event be planned around when SD is there but he has backed off since then. I think some of it is that he is afraid of being judged if she isnt there. But the reality is that she is going to be gone for alot of events because she lives half her life outside of our household. My parents also overcompensate because they dont want to be seen as the evil step stereotype. Its really annoying. Theres a difference between being inclusive and making everyone revolve their lives around one family member.