My dad is 97. His long time companion is in rehab hospital. He went downhill within a few days. He has been inappropriate with staff. He is angry he can't stay with her and mentions it every few minutes while awake. He is not fit to drive but insists he can. His primary dr prescribed aricept. After one dose , he woke up at 5 am and accused me of kidnapping him so he can't go home. Wondering if we should give him another dose.
If his companion is in rehab, I'm assuming that she would be returning home after Medicare pays its portion of rehab, and they could be reunited.
Try redirecting his attention to supporting his companion, with cards, or phone calls, and consider how they could celebrate when they're re-united. If his attention is redirected to support for the next 4 weeks or so, and for a nice reunion, he can focus on that. Perhaps help him plan a "reunion" party for her return home.
If you can visit, you could also bring her cards to deliver to him; that would help him keep in touch with her, from her position.
Another aspect to consider is home care post rehab facility. Can he help with arranging for that, such as contacting home care facilities and getting information? (You could prepare a checklist for him). He could also consider what home arrangements might have to be made before and/or when home rehab starts...removal of rugs, installation of grab bars, life alert pendant, etc.
This article says that Delusions are a side effect and not recommended for someone who had Dementia. You need to call the doctor who prescribed it.
Your Dads Dementia is your problem. He has lost the ability to reason. All he knows is he wants to see her.