Nope.  It was wrong of your fiance not to discuss the date of the party with you.  I'm sure he's saying it's not a big deal because HE SCREWED UP.  It's obviously a big deal to you.  He should be apologizing and trying to figure out if there's a way to make this right, not acting like it's not a big deal and you shouldn't be hurt

That's so wrong. My husband would never plan anything let alone something that huge without checking with me first. That's very hurtful esp after you told him you can't be there and he doesn't care. Ouch. 

I get annoyed with my SO for only informing me of SK plans after the fact & not including me in making them. He does give me notice & he does consider my schedule but I still think, after a number of years together, I need more than the bare minimum. We should be discussing things & informing everyone else - he no longer needs to be discussing everything with BM or whoever & informing me. Your FH hasn't even given you the bare minimum! Is he just going along with what BM wants, does this date suit her, so he's good with it & everyone elese be damned? Also, if it's a big deal to you, it's a big deal. What a jerk.

Inconsiderate to the max lady.

All your efforts were just thrown back to your face.

Let the numero uno family party on. As for you DO NOTHING for anyone, you were just shown it does not count. You were shown you are the outsider, the help, an after thought and truly not even that.

I would be fierce in my anger towards DH. Go on strike from here on.

parents co-exisiting to the point that they have a joint graduation party, he should have involved you in it's planning. I'd be miffed too.

Please make suer the boy understands that you really wanted to be there but cannot and explain about your work. He's old enough to understand about responsibilities. Do it soon so he does't go thinking that you just don't care.

I think it's unfortunate that your SO didn't have a set of dates in hand that would have allowed you to attend this celebration.  It sounds like you have a good relationship with your SS and it does sound like you will at least be able to attend the ceremony.. so there is that.

At this point, it's going to be tough for your SO to shift the dates.  It's quite unlikely that his EX will be all considerate of a proposed change when he tells her that you are the reason.  

To be clear, this is either a bonehead move of a SO that is otherwise a supportive partner.. or I guess he could have intentionally picked this day so there wouldn't be the akwardness of you and the ex being there?  

I think I might be inclined to take it in the most positive way possible that this was an unfortunate oversight... and changing it is likely not going to be possible.  I would see if you and he could work out a special celebration with his son separate from this larger party.

I agree with ESMOD, plan something special or a mini weekend trip with you, DSO, and SS.  

Our graduations are on Memorial Day weekend for the whole county.  This way, more out of town family can attend since it is a long weekend.  Maybe it was the only time the bio family could do a grad party and that is how it is sometimes.  

I raised my SD for 7 years but let her and BM plan the grad party (but I didn't want to go).  I also worked many nights and weekends in my career and missed many of my own bios big things.

Yeah, that's crappy. I'd be inclined to do absolutely nothing for the party other than get SS a gift. 

He doesn't have your back

But figure out a different way to celebrate with SS.

Let your Fiance know this was something that upset you. Do nothing for party, just plan something private for yourself and SS. You know that you helped him through and you did it for his benefit. We do not get the glory, but we get the love.

I am sorry.