Dear McKoy: I Think My Girlfriend and Her Half-Brother are Having Sex

Dear McKoy: I have an issue that has been bothering me for a while and I don’t know how to approach my girlfriend with it. We are in our early twenties and have been together for two years. She has a half-brother who is 24 and I think they are having sex. They share the same father, different mothers, but were not raised together.

When I visit her, I always noticed that they act strangely around each other, too flirty for a typical brother-sister relationship. Sometimes he makes so obscene jokes, slaps her butt, she laughs and seems to enjoy it.  They exchange small glances and whispers that appear to be more than just affection, she even sits in his lap sometimes.

Last weekend,  I went to her house and found him in his underpants and to the looks of it, he had a hard-on. This even gives me more reason to believe they are having sex.  Their behavior is not normal, I have a younger sister, and I would never bring up anything sexual with her. I have not asked her about it yet because I think she may lie to me or if my assumptions are wrong she may want to break up with me.

Do you think I’m being paranoid and jealous of their close relationship? I feel like I’m going insane and I can’t even have sex with her without thinking about them together.  Please advise.




Dear Michael: Having sex with a blood related is considered incest. When blood relatives grow up apart and subsequently meet, they may develop an abnormal sexual attraction to each other, which does not occur when siblings are raised together. It’s referred to as “genetic sexual attraction”.  However, you’re not certain your girlfriend is having sex with her half-brother. It’s possible you’re wrong and they are just a family that shares a close bond. 

The risk of getting it wrong might ruin, not only your relationship with her, but also her entire family. Speak with your girlfriend. Tell her that you are bothered by her behavior around her half-brother and believe it is inappropriate. You don’t have to accuse her to figure out what’s going on. 


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