This has happened before with us. A demon may become sexually or romantically attached to a human, but normally they are Succubus or Incubus, it has happened with others.
Our own case was with a 'servitor' demon. He looked upon us like a child, but once he saw what we were capable of, he suddenly wouldn't leave...like at all.
Normally, keeping love-block herb mixtures or binding the spirit away can get rid of them.