I'm asking this on behalf of my partner, as he's asked me to help him respond to his half sister.
They both share a father. My partner was not brought up by his biological father and only started having contact with him after he turned 18. They talk on the odd occasion, and once a year we might go to visit him (it's about a 3 hour drive). We always have to make the effort, not him.
As far as I'm aware the half sister had more of a relationship growing up, but he wasn't always present.
My partner didn't realise his half sister (who is older) existed until a few years after he started having contact with his biological father. He and his sister connected on FB and exchanged messages for a couple days, then stopped, this was a few years ago. They've never met. At the time the half sister was in contact with the father, and had more of a relationship to him than my partner.
Last week the half sister messaged my partner after a few years of no contact asking if he'd been in contact with their father as he hadn't been responding to her texts. My partner told her he hadn't messaged him in over a month. She explained that they had a falling out after she had told him some home truths and he did not like them. My partner has since heard from their father and so told her that he has, saying that they spoke briefly and maybe he was busy when she was trying to message him. To which she replied
"Okay thanks. He's ignoring me then. Hope he's a better dad to you than he ever was to me".
My partner is lost for words. He wants to reply but doesn't want to upset her further or make it feel like he's rubbing it in that their father will still talk to him and not her. He doesn't really have a relationship with their shared father, and he hardly knows him. He considers his step dad his dad and only ever refers to their shared father by his name. How could he respond to her in such a way that he's expressing sympathy for her and not rubbing it in that he still has contact?