The main character is likely the ladies man. There may also be a few key women in his life who play important roles. These women could be of different personalities and backgrounds, and through their interactions with the ladies man, the story unfolds. For example, there could be an innocent young woman who is charmed by him at first but later realizes his true nature, or an older, more sophisticated woman who tries to tame him.
In 'Death of a Ladies Man Novel', the most prominent character is no doubt the ladies man. However, there might be other characters like his friends who either encourage or discourage his behavior towards women. And then there could be family members who might have an influence on his view of relationships. Also, there will probably be some of the women he has relationships with, each with their own story and motivation, which together form the complex web of the story.
I'm not sure specifically as I haven't read the novel in detail, but surely the 'ladies man' himself is a main character.