With my SD I went to the ones I could make(back when she did cross country).  DH would go to the ones he could make and BM..she refused to go to 90% ..worried she would see us there (she couldn't handle being in the same space for several years).  
i don't think you are being selfish.  Any kids sports stuff can get crazy.  

Your spouse is the issue.    He's dumped skid on you.    Now you are recognizing the bad deal you have been given.

Amd of course now if you say something you'll be gaslighted and they will be incredulous about you not wanting to be the babysitter..

There are plenty of bio parents who drop the kid off and don't stay for the games. Especially if there are multiple children, parents can't or don't want to spend all their time like that.  It's even simpler for a stepparent - it's not your child, so chances are the skid doesn't care all that much if you're there or not. No reason to feel selfish - you do way more for this kid already than either of his parents. 

Your H has unrealistic expectations if he expects you to be at every skid event,  especially if he doesn't go himself. Pick and choose what you want to stay for.

"step child lives with us therefore I do all the school runs, random events, friends, parties and stay until it's over and  what ever  pick up dropp off you name it along with raising him since he no  longer lives with his mom"

Why does the step child living with mean that "therefore" you do all the parenting?  As a step parent, you can volunteer to help out but this stuff is 100% the bio parents responsibility.  

In reality it should be "step child lives with us therefore his BD does all the school runs, etc and I help out when it works for me".

I'd be tempted to ask your SO for a paycheck if he wants you to do all the childcare but only if you want a second job.  Hope this doesn't sound harsh but does he think this is womens work?  (Sorry, I'm finding the fact that he expects so much from  you slightly triggering)

Decide how much you want to help your SO and don't do an iota more.  Your SO is a grown up and will figure it out.

THIS

And TAS said it much more politely than I would have done.. You are the kid's father's wife, not his mother. Anything you do, you do because you choose to do it, not because you've been guilted into it. You have your own life and don't need to be running after someone else's kid instead just because his father thinks you should! Stop doing his job for him NOW! 

No.

I attended SDs events, the bigger ones, when they were younger and I lived closer. As they got older they did LESS so less events, and they would specifically ask DH to go but not me. So I just stopped. No invite or interest in me going so nope. Especially after YSDs last event that was a horrible ending. I was 100% done.

When Chef used to subscribe to the "One big happy family model" (TM),  he would get all excited about his kid especially the oldest enrolled in football et cetera. 

Chef is very athletic but the skids took after the clumsy non athletic Girhippo.   He would say dumb things to me  like "your ass is going to be on that bleacher seat every Saturday and Sunday all day."

Well I went religiously for the first few years, enduring the stink eye by the entire community that the Gir had poisoned against us  to the point of being screamed at and hung up on by one of the coaches (one of Gir's flying monkeys) just for asking for a schedule.  This was before the Internet boom  and online schedules abounded.  

 Then there was the time when OSS was enrolled in wrestling and wearing one of those wrestling suits that was 4 sizes too tight and looked like Borat. 

Chef tried to calmly give him pointers but OSS screamed at him to leave him alone  (picture oversized, too tall michelin man  ginger in orange Borat suit turning purple with rage)   It was  a giant intramural gymnasium and you could have heard a pin drop after that display as the result of PAS.   Extremely embarrassing for Chef and me for him.

 When it was clear to me that the ferals,  who were signed up for every activity under the sun,  were not taking sports seriously but just using it as a social occasion and to showboat, I slowly stopped going.

Just out of curiosity, Renahemleezy,

In your previous posts, you indicated that your stepchild was female yet you now indicate that the child is a male. Additionally, you failed to respond to any of the queries from the members that were attempting to offer advice. Whassup?

I agree this is just a forum, but perhaps they were just confused on the situation? I know my family is a yours, mine and ours situation  and at times would be a good jerry springer episode! Everyone's story is complex because life is complex-you don't have to write or explain anything you don't want but for some it's easier to relate or give good advice when they better understand the situation perhaps?...life is crazy. Just  food for thought

Yikes, hregal2011,

I did not intend to plagiarize your excellent post! As it happens, I submitted my own offering before closing and re-opening Steptalk so was not aware of your earlier reply to OP.