Brotherly Unlove?

My sister Sophie, apparently, has a new girlfriend! It's her first 'proper relationship' since her 'unpleasant uncoupling' from Tamara back in God knows when, and I only know about it because Philippa let slip a little comment during a conversation about lasagne (of all things). Philippa insisted she wasn't supposed to tell me about it, but when I pressed her for further information, she crumbled like an Antarctic ice sheet. They met, shockingly, through a dating app. I say 'shockingly' because my sister is even less of a fan of technology than I am, and because I didn't think those online dating algorithm thingies ever worked. They had their first 'meet' back in November and have been growing closer ever since, and have now decided to make it official, and make a go of it. (But without making it 'official' to me, obviously.)
I'm pleased my wife is terrible at withstanding gentle interrogation, but less happy about the fact that my older sibling didn't feel she wanted to update me. If anything, she was actively trying to keep the information away from me.  Am I really that bad of a brother? Does she think I'm going to pollute the blogsphere with lurid details about her private life? And why does she trust her sister-in-law, whom she has only known for a handful of years, more than she trusts her own brother, who has been in her life since his own first started?

I put those questions quite firmly to my wife, who said, "Well, maybe that's something you need to think about."
She also said, "Don't tell her I told you or she'll think I'm a snivelling weasel." I'm not sure that's true, but I have to say I think 'snivelling weasel' is a fantastic name for a rapper.

RC 11-2-23