I have been a step parent for 9 years.
I have SD14, SS13 and SS11. I also have DS12.
The early days were wonderful. I'd always wanted more than one DC and had been unable to. To see DS interacting with his step siblings was, and still is, so wonderful. They've made his childhood so much better than it would have been otherwise.
I had a brilliant relationship with them all, particularly SD, I'd be lying if I said I didn't love the girly side of it - braiding her hair, picking clothes, crafting. It was very different from time spent with the boys which was mainly gaming, wrestling etc
But the later years have been fraught to say the least and I've frequently wished I'd never even met DH, whom I love very much, that's how bad it has been.
My stepchildren's mother is difficult. She always has been. She's no interest in any kind if relationship with me, which I know is her choice to make but its made it hard on the DC. SD now hasn't spoken to DH for 4 years after being poisoned against him by her mother. SS1 has autism which has become more apparent as he's gotten older and has led to some meltdowns and sometimes I've been afraid. He's 6 foot now and I've sometimes felt I have had to leave the house to be safe.
SS2 is completely obsessed with Fortnite, plays it constantly and seems all he wants me for is V bucks. DH has cut the Internet off a couple of times but all SS2 does is walk out of the house and go back to his mothers.
It's very tough. I'm thankful to my SC for the sibling relationship they have shown to my DS and I do love them, but I can't say being a stepmother hasn't been one of the hardest and most thankless things I have ever done.. because it has.