Lonesome - Sad or dejected as a result of a lack of companionship.
Merriam Webster Dictionary

Looking up the word, lonesome, Ben knew it was lonesomeness that had been his living companion for nearly half his life. His dreams of Theresa began at age 15. The dream turned sexual the following year. Theresa became his fantasy girl, the one who supplied all the masturbatory imagery needed. Sam supplanted Theresa in his dreams following their chance meeting at the hospital bedside of his sister, both simultaneously experiencing an electric jolt at their first touch. The first time they made love, both realized predestiny was at work. Their wish to go slow proved impossible, their love all-penetrating, the sex perfect.
Events soon got in the way. Someone was trying to kill Ben's sister. One attempt resulted in Alex losing her unborn child, devastating her. Blaming the loss on her husband drove Tom into the arms of the woman who had craved Ben since high school. Linda lived on the edge by choice, an edge that would eventually make her a brain-dead-incubator for her unborn child, whose father remained unidentified. Tom was but one possibility. Then Ben met Maria, Theresa, personified.