My question is, if they don’t remember their SPOUSES, how do they remember each other??
He may be living in a time before he had kids or was married to his wife. Everything needs to make sense in that time frame, or the patient gets upset. To me, it was as though the mind was striving to force sense into a nonsense situation and anything that helped was accepted.
Seeing his girlfriend all day every day helps keep her in mind. Also, he's not married (in his mind), so it is natural to have a girlfriend. It makes sense.
My dad sought things that would make sense to him and angrily or emotionally rejected what did not.
Eventually, he won't remember the girlfriend or anything or anyone else. But for right now, at this stage in the illness, it is as though the mind reaches out to grab anything that helps it cope with the perceived nonsense. If he knows he is 20 and unmarried (or whatever), why does the rest of the world say different? Having a girlfriend helps that.