Well, I had a suspicion. She had started tickling him and rough housing with him. I asked her what the nature of the relationship with my son was. She smiled and said, "Oh please don't worry about anything like that. He reminds me of my little brother and I miss my family [her hometown is about 1500 mi away] and he just makes me think of what hubby must have been like when he was young. I love him like a little brother."
A few days later I had to go out of town for a week. A few days after I returned I overheard my 2 boys fighting, the younger one  told his big brother to go away and leave him alone or he was going to tell mom and dad what big brother and my gf were doing. Big brother became very angry and shoved l'il bro's desk over and went off angrily to his room. I cannot describe the pit in my stomach. They had no idea that had overheard anything.
I waited a few minutes and went to l'il bro's room and started helping him clean up. As we were putting things away I told him I had heard what he said and wondered if he would tell me what he meant. With hesitation he told that he heard something. When I asked what he heard he said he could hear them doing it. (My God, who knows how long he would have carried this secret with him). I said what exactly did you hear? He said he could hear the sex noises coming from big bro's bedroom and she was in there. I didn't push for any more details, this information was enough for me to know that it was time for her to leave my family.
When I opened my mind my heart got bigger.
When we place preconceived expectations on those we love we neglect to consider their individual goals, needs and desires. We fail to respect them and love them for who they really are.