My mother married twice. 5 kids with first husband, and just me with the second. 8 yr age gap between me and the youngest of the 5.
They have never once let me forget that I am "only" a half-sister whereas they are all siblings.
All my life I wanted them to accept me and include me in their family. They never have. They have over the decades routinely excluded me from parties, meetups, holidays, celebrations, etc. One of them bought a timeshare holiday home abroad and over three decades invited all of the others in turn to use it. All I got was to hear from the others what a great time they had there; I was shown photos of them having a great time there. I was never once invited.
Three of them have been so nasty and cruel to me that I am now NC.
The other two, well, we are "on paper" still on speaking terms but they never contact me or invite me anywhere.
It wasn't my fault that I was born. It wasn't my fault that my parents had only me. I think my half-siblings should have included me in their family, and not made such a huge distinction based on whose sperm they came from. We all had the same mother, after all.