I think you’re getting a hard time OP.
from reading only your responses I get the feeling your Oh prioritises his 1st and you and other children come second (in your eyes) and though you have accommodated in the past..and probably been taken advantage of - you’re fed up.
The whole “you knew what you were getting in to” statement constantly thrown about is boring and ridiculous so take that with a pinch of salt. What was life 7years ago isn’t anymore.. there are now 2 further children involved.
as a stepmum to 2 (now adults) I was the one who involved them with everything, mine went without as we did very little the weekend we didn’t have SK so that they constantly felt involved but that changes as years go on and they all grow. If it’d been my 30th I’d have wanted them there, if it didn’t work for Bm then so be it but they were always asked.
i don’t understand the 7pm pick up being that much of an issue unless you both have to be there at bedtimes every night?! So I do think some adjustments can be made by you all. That being said, just because it suits BM doesn’t mean it HAS to suit you.
personally, your OH sounds like a good dad. I think he’s probably making up for not being “present” daily with his 1st but that doesn’t and shouldn’t stop him from being present and there for his others too. Could he take the others along to eldests football? Take them all to the park?
do you really do nothing when eldest not with you? Does he always reference it if you plan something without him? I think you have to have your own lives too.. whatever you guys are doing probably means eldest is doing something else in his other home?
I’m no expert but what was a very easy first 8years of being stepmum very quickly turned and ended with a decent 2years of hell (not on kids part) and becoming a stepmum full time from there on in…with no weekend visits so from 1 to 3 children. I’d not change that, I’d change the malicious, manipulating, vindictive BM though !
I think you have to decide if you want to be with your OH. You need to decide what and where things need to change. Counselling maybe? You’re not horrible, you’re navigating 2 families…