all the other posts are irrelevant anyway as they obviously can’t relate properly.
You don't need to be a step-parent to imagine to needs and feelings of a nine-year old whose parents are living apart.
Nobody has suggested that it is easy to treat step-children equally to your own children and it's pretty much obvious to any parent that you are going to love your own child more than a step-child.
However, you are an adult who made the decision to become involved with someone who already had a child and become a member of a blended family. The little boy you're talking about has not made any such decision. With the right to make that decision comes a responsibility to make his well-being a priority, along with his sister's.
Your stepson needs to be welcome to participate in family life just as much as he would if he was resident with your DP full time. You hold some of the responsibility for meeting that need, even if it isn't something you want to do.
If this little boy is excluded from the family holiday abroad every other year he will feel resentful. Imagine getting home from a lovely holiday, feeling sad that it's over and knowing that you won't get to do it again for two years but your sister will get to go on the next one. That gives a child a very strong negative message.
You need to stop blaming your stepson for the harm his parents have done to him and for the irritation his mother has caused you. Out of everyone in this scenario, he is the most vulnerable and he deserves to be protected from further distress.
Your feelings and your words/actions must be separated. Thinking that you'd prefer a different arrangement is something you can't help. How you respond to those feelings is what matters. Stop fighting to exclude your stepson from important events in his own family and look for ways to make him feel welcome instead.
Struggling to discipline a child like your own coz he’s not your own... worrying what your allowed to say!
This is something you need to work through with your DP. While this little boy is with you, there need to be clear and consistent boundaries for both children and you and your DP need to be in agreement on what those are. You successfully co-parent one child already so it shouldn't be too difficult to work out how to apply similar strategies for your stepson. Having these expectations and boundaries in place is key to you all being able to enjoy holidays together and it will get more important as the children get older.
YWBU to continue to push for holidays which exclude this little boy but you need to find ways to work together with your DP so that you can all find holidays together enjoyable.