About 6 mos ago my 82 yr old father starting questioning my mother (81) who she slept with and who her boyfriends were in high school; which then turns into arguments. They have been married 60 years. He will not let it go, he just keeps on and keeps on asking her stuff and accusing her of what he thinks she did in high school. He will not say or do anything when any of us are there. We addressed it a few months and he just shrugs it off. Mom is not in good health and he takes care of her on a daily basis and usually all goes well. Until he gets it in his head to start accusing her of "sexual" things she did in school and with you. Any advice?