The suffix “er” i.e. “Engineer”, means “a person who executes X”, where X is the root.
The suffix “ize” i.e. “Fertilize”, means “a noun which adds the property / transforms something into X”, where X is the root.
“Womanizer”, then, means “A person who adds the property / transforms something into a woman”.
“Womanizer” is a word interchangable with “Ladies’ Man”, that is, a man the ladies like, and is used most often by those women who fail to get with the man in question or men who fail to have the success of that same man.
Women love “A person who adds the property / transforms something a woman”.
What could be that something?