I have a cousin who goes to church every Sunday, but is living with her boyfriend. When confronted about why she is having sex outside of marriage when that is against her religion, she replied, “I don’t think it’s a sin.” The problem is as old as Eden...people deciding good and evil for themselves.
And your cousin is wrong, clearly….on this point. But I would be hesitant to say that this one thing makes her a false convert, or a sexual atheist. That may be the case, but I would narrow the brush a tad...