Step Children threw DH a 'special day' party and did not invite me.
I've been married to DH for 15 years. His children were teens when we first got together. I tried for several years to be nice to them, but after many many many disrespectful acts on their part, I stopped trying to be nice, and probably was obviously so, so I know some of this discord falls on me. A few years ago after some especially distasteful episodes, I told my DH I didn't want anything to do with his son. Some months ago I said I was willing to let bygones be bygones, but DH said I had to apologize to SS - He says I'm the 'adult' (kid is almost 40). This will not happen!
So just recently, SS and SD had a surprise 'special day' party for DH at a local establishment and purposely did not tell him about it in advance because I was not invited, even though many of DH and my friends were invited. When DH got to the party and saw what it was, he decided to NOT call me and let me know to come to the party, since they had obviously not included me. He told me after he got home and filled me in on the event that he didn't want to get in the middle (in other words, he did not want to stand up to his rotten kids). So it's OK to hurt my feelings, but not his 'kids' feelings. Plus he sees them several times a month, so it's not like he can't have time with them. I encourage it, just not on Friday nights through Sunday morning.
When DH and I are together on vacation or other places with our friends, things are mostly OK. I just have such a hard time knowing what to do when it comes to his 'kids' (they are both in their 30s with no significant others) because I know they will always 'win'. It's hard to disengage myself entirely.
The comments in these forums are very helpful, however I've still found it very difficult to not get upset about these types of incidents. I'm very close to just ending the marriage to get away from it.