erotomania - look up the meaning of this. Years ago I had a friend who was totally convinced she was in love with the vet that treated her horse. He was in love with her to apparently but couldn't tell anyone because of his father who was in a position of influence. Thing is she was totally convinced this was true and nothing would convince her otherwise. The poor vet was oblivious.
She told her husband that she was leaving him for this man. Husband came round to ask me what was going on and said he felt like going to see him and stick a knife in him!!
I didn't know what to say other than said man would be really shocked because it wasn't true.
There is a lot more to the story but would take me forever to explain. Suffice to say we are now 20 years later and she is still convinced it is all true. Despite fact that man married someone else.
Apparently this condition is incurable :(