Your husband is not thinking logically. I would never have missed a graduation of my beloved nieces/nephews (nor did I) to attend my SD's graduation. Family is family and the old adage, 'blood is thicker than water' will always be true.

 It's unfair for your husband to expect you to attend his child’s ceremony and disregard that of your nephew. Hon, don’t accept any guilt trips on this topic! Perhaps you could consider taking the girl out for dinner the following day to celebrate her accomplishment?

A lot can happen in a year and who's to say if SS walks?  IMO he's starting his game too soon.  

Without hesitating, I'd choose my nephews over DHs kids. Like you, no bond. Even moreso, no relationship with DHs kids after over a decade of tolerating their crap behavior. I completely disengaged about 6 years ago and have only seen a couple of DHs kids and very short interactions. I refused to attend a wedding of one of his kids and I refused to attend birthday parties of kids (grands) I was shunned from. I mean, the invites were only to appease DH and I refuse to go anywhere I KNOW I'm going to be treated poorly. 

It's mind boggling how these men can even THINK we'd give up our family over their troublemaking kids. SMH

Wants you in the BM role As in his family is the same as before divorce but remove the ex insure you, Happy Family [ what was never happy]  goes on.   He wants you to be that person, but knows you can't be. That's upsetting to him.

IMHO it is about the quality of the relationship and the demonstrated quality of the graduate.  Quality gets the attendance at their graduation.   The challenge comes in when both kids who are graduating are good kids and have mutually respectful relationships with the invitees.  That makes the choice of which to attend extremely difficult.

So far, we have not had that conflict.  In fact we have had no conflict because no graduations have coincided.

There have been a few graduations in my IL clan that my DW attended and I did not. Though not out of conflict with another graduation.  I go when I can fit it in around work.

An interesting juxtaposition regarding what follows a graduation.  In my IL clan  the graduate peaks at graduation then commences a long glide path of degrading life struggles.  My  DW has been the only one to grow rather than degrade after gradation.  In my family graduation is a beginning to a long journey of accomplishment. 

One side there is drama and a hollow superiority complex that focuses on manipulation, attempts to embarrass others, and has this air of smirk at the person who is not going down the well worn path that everyone else has gone down ad infinitim. On the other  side there is true love of family and a dedication to making a future rather than eternally repeating a past. that has a vein of sadness about it. 

My DW makes our family name that much better.  In her family, she has been told that she intimidates her sibs and much of the extended IL clan family looks at my DW and me as some kind of idiot snooty relatives while we are the only ones without multiple foreclosures, reposessions, and bankruptcies.  We have never had even one..

I truly hope that kids who are graduating go on to lives of love and accomplishment rather than a sad replay of the failures of their families.  Even when there is that history, there can be a different choice.

My DW has certainly proven that.  

One of my life rules since entering steplife is to spend my time and efforts with kind people who mean something to me and to whom I mean something,

I was a slow learner, but it hit me one day that life is too short and I was sick and tired of being one of those old blowup clown punching toys. Oh! Now I have an accurate idea for a profile pic!