I also hear people make the same claims against Alexa, but I usually start explaining what cookies are and how ad networks collects your data to more effectively target you. It doesn’t make fiscal sense to do mass audio surveillance when you already freely hand over your data.

Most likely this. If not, there is a host of other possibilities they could make the connection. Sone that come to mind:

• You both have instagram and have connected in a way that makes it likely you are in a close relationship (tagged in photos, DMs)
• She allows Instagram to access the contacts on her phone, and OP is saved in there as her S.O.
• They are connected through Whatsapp or some other Meta service.
• The Company targets their ads at category which they both fall into (companies can manage which groups see their ads VERY specifically)
• Coincidence

Between this and geolocation I'd say its not hard to figure out you guys are in the same house

It's basically always this. Your phone in the same room with someone else's phone. This is stronger around christmas when people are looking for gift ideas, so they push this mind control shit on you even harder.

It's not actually listening to you--that's been debunked multiple ways--but what it's doing instead is arguably worse.

So what are the mechanics of this? OP would also have had to interact with Meta somehow after finding the moccasins but before the girlfriend did, right?