Like in the title can a succubus be loyal to her lover or it has to have sexual intercourse men?
This question is not as fairly easy to answer as what you can expect. One of the huge problem we have is "succubuses" (or "succubi") are not well defined creatures.
We have two main Hebraic sources:
- The Alpa beta (or Alphabet of Ben Sira): That book is the one where the infamous Lilith appears and let's face it, this book is a giant troll book.I linked to you an analysis of Lilith I gave some time ago.
- The Zohar: Another questionable book, certainly less than the AB, but still, cf the link I gave. There we find such demons, named the four queens of Hell (Lilith, Agrat Bat Malhat, Naamah, Eisheth Zenunim).
What we can see here is: Succubuses are clearly defined as female demons, and in the Zohar they are simply the mothers of all the demons (except Lilith, which is sterile). The Zohar is vastly used to build the Kabbalah, but sometimes it is a book difficult to understand or "follow" as I shown in the Lilith's answer.
Middle age sources
Middle age is a "funky" time where people was debating over such questions as "Can God defecate ?" (yes they did). And during Middle Age there will be a lot of discussion on the nature of the succubuses.
The question of the sex and ability to reproduce of those demons has been question over and over.
Thomas of Aquinas suggested that succubuses and incubuses was a unique demon, switching sex, stealing semen as a female over human being male and using it on female to impregnate them. Merlin, in the Arthurian cycle is such a man (The usual name of such an offspring is 'cambion').
In the Malleus Maleficarium, another infamous troll book (this time in the very bad sense, because it has been quite read), the anti-witch book by excellence. In this book the succubus will steal some semen to human male, give it to an incubus (or shift into an incubus, depends) and impregnate a woman given her malformed offspring.
In substance Middle Age denied angels and demons any reproducing ability. But linking those demons with high sexual perversion they tried to find way to explain that.
Now concerning purely your question, considering the small sources we have, and the fact they are often to be taken carefully, we have such a story with the "pope of year 1000", Sylvestre II, Gerbert d'Aurillac.
Gerbert of Aurillac
Gerbert d'Aurillac was a fairly intellectual man in Middle Age. Because, as lots of Middle Age mathematicians, he took a great care studying muslim mathematicians, he was not so loved (he is one of the first men in Europe to use arabic numbers, way before Leonardo do Pisa, Fibonacci (roughly 200 years)).
Walter Map's De nugis curialium
The story of Meridiana is known to us by Walter Map's De nugis Curilium written way after Gerbert's death.
He is supposed to have befriendeded a succubus Meridiana. She is supposed to have been her "dark council" and completely helped him to become the Pope. She is known to have warn him to never preach in Jerusalem. He unfortunately prayed in a church of Jerusalem. that is a clear example of a succubus showing loyal love to her "mate".