This in fact happened to me. He was 22 years older than her. And basically living at my house except when I was home. Has there been any change in his behavior since meeting her? He completely changed. My daughter alerted me to the situation. Confronted him and he said she is my best friend. Hmmmm....best friend that I never met, but is at my house everyday. There's a lot more to the story. But I know how you feel. I know exactly what you are going through and if your gut is telling you it is wrong...it probably is.