Why does my husband of 50 years get jealous when he sees my “boyfriend” in the house when there is no one there?

I agree with Jeanne. It could be early onset Alzheimer's or other dementia type condition, or medication interaction. If this behavior has come on suddenly, I would have him checked for a urinary tract infection, or other medical condition. If he doesn't want to go to the doctors, have the doctor call HIM and ask if "he can come in to update their records"

If you have 'pictures of other MALE family members' even, him and you in earlier years, be mindful that THESE can be the 'other men' in the house! Even too many MIRRORS can have an adverse effect on those with dementia. They will 'see' people in the house (when it is really themself) and think others are in the house.

A medical exam is in order, preferably one that is well versed in geriatrics.

I do hope this helps!

Yes, it is a mental problem. If he sees people in the house who aren't there, that is hallucinations. If he believes things that aren't true and which he has no evidence for, such as you having boyfriends, that is delusions. Delusions and hallucinations can be signs of dementia or declining mental health. They can also be symptoms of other problems, such as UTIs. Has this been going on long, or is it new behavior? What other changes have you noticed?

It sounds like it is time for a thorough geriatric evaluation, to see what is going on with your husband, whether there are any treatments to consider, and to get an idea of what might lie ahead.

Best wishes to you.