"Devil's Keep", a novella by Rebecca Brandewyne, was published in the 1992 paperback anthology Bewitching Love Stories from Avon Books. The cover matches your description. The other stories in that book are "Vanquish the Night" by Shannon Drake, "My Aunt Grizelda" by Kasey Michaels, and "What Dreams May Come" by Christina Skye. That last one is your story about a woman who falls in love with a ghost.
The stories are described in the following Amazon customer review by Marilyn Rondeau:
Devil's Keep Rebecca Brandewyne 5*
This was a real sensual delight and so worth the entire book - although the other stories were very, very good. Count Drago von Reicher puts an advertisement in the paper for a governess for his son. Lenore Blakely answers the ad after being turned down so many times before due to a lack of references from former employers. It seemed that wives did not look kindly towards beautiful governesses once their husbands and sons were effectively rebuked by Lenore. She is hired sight unseen and without an interview by the Count - her first inkling that something might not be right. But, considering the fact that she was close to being totally impoverished, she accepted the position. Upon meeting her employer, the extremely dark and enigmatic Count, her first instinct was to run, but after gazing into his eyes this soon became an impossibility.
The reader as well as our heroine is then hooked - pulled into this devastatingly sensual adventure to mind boggling delights of the senses. The love story here transcends all time and is truly fabulous for such a short novella.
Vanquish the Night - Shannon Drake 4*
Colonel Michael Johnston, famed war hero and Indian fighter felt the evil coming into the night on the cool breeze, but never imagined it would be a fight for the very survival of the woman he loved.
Anne Pemberton was a descendant from a very strong woman, one who committed suicide rather than live with evil. The very handsome and enigmatic, David Drago had searched for centuries to find Anne, the one woman he would take for his bride to live in the darkness and evil that was his domain. It took all the faith and love Anne and Michael had for each other to face down and destroy the vampire - proving that love and faith could conquer evil.
This was a very fast and sensually written read with this time, a very bad type vampire! Good story.
My Aunt Grizelda by Kasey Michaels 4*
I really liked this story which kind of reminded me of Cinderella and gave me visions of the very inept and bumbling witch from the TV series Bewitched . Do you remember Aunt Clara? As you read this delightful story - Aunt Clara is pictured quite vividly in my imagination. The sensuality is minimal in this story of the governess who falls happily in love with the Earl, but the laughs are numerous. Ms. Michaels witty dialog is delightful and this story is quite like reading a fairytale. But I do believe in magic and fairytales so - Yes - I liked it!
What Dreams May Come - Christina Skye 5*
Re-enter the ethereally beautiful world of Draycott Abbey, where Adrian Draycott, the resident ghost and caretaker resides with his ever faithful companion, Gideon. Once more, Adrian has been awakened with feelings of danger in the wind. He is feeling depressed, ever since he had helped his brother (in one of his many incarnations) find his way back to loving his reincarnated soul mate. With Nicholas and K.C. on their honeymoon, he is really annoyed that a woman has entered his precious Abbey. More annoying is the fact that without trying, his ghostly being has become quite real, flesh and blood! And, this woman has aroused in him feelings in his, shall we say, man-parts, that haven't been aroused in centuries!
Who is this woman, Gray Mackenzie? Why can she see him, and touch him and arouse him to such a fever? What is the secret she hides, and why can he not remember who she is? In this very, very sensual offering from Ms. Skye you are in for the treat of your life as you experience a most ghostly affair! Dynamite love scenes that will curl your toes! And of course, there is Adrian, my own personal dream of who I'd like to haunt me! Super read.