Not intending to brag. I discovered recently that a family member has given us £10,000 - not once, but twice. Once recently, once 6 months ago. But my DH apparently hasn't thought it important enough to tell me about it.
We're not so crazy rich that this wouldn't be a significant amount of money. The account it went into is a joint one, but I rarely look at it (maybe I will more in future!).
DH did say early this year that family member had suggested they might pay something towards the cost of something specific and I said I wouldn't have a principled objection, assuming he meant 1-2k. He never said any more, so I assumed nothing had come of it.
The second payment appears to be related to an inheritance from a family friend, probably left to our family member. I knew nothing about it at all.
We've been married 20 years and I don't get on with said family member. DH has previously promised not to share confidential things with them about our family that I don't know about. I'm not very happy that I've not been aware (though obviously happy to have the money).
YANBU - most people would tell their spouse.
YABU - it'd be reasonable for your spouse to keep this quiet.