I see from your later posts that you have accepted that YABU, so I won't go on about the sibling issue, but I did want to let you know that there are many step parents who continue to have a relationship with their step children after their relationship with the biological parent has come to an end.
My own biological father left when I was 2, and I have only seen him a handful of times in my life. However, when I was 4, my DM married my step father (DSF), and despite them divorcing when I was a teenager, he continued to be an important part of my life. I'm now in my 40's, and DSF never had any biological DC of his own, but to me he is the best Dad I could ever have hoped for. He's been there for me through everything, has helped me in emergencies, looked after my DC when needed, bailed me out of problems - everything a biological father should do for their child. My DDs call him Grandad, and I've always called him Dad. He's in his late 70's now, and has recently started to show symptoms of dementia, which is heart-breaking, but he knows that whatever happens, I will be by his side because whether we're related by blood or not, he is, and always will be, my Dad. No tattoos though, sorry!