I would never be able to sleep with a man again if I knew he had been going at it with HIS MOTHER... It is just WRONG. This is a taboo that is actually there for a reason, unlike many others (like interracial or same-sex before, cousins still) because it is mentally damaging and it also affects any offspring. Now, if he is in his 40s his mom is clearly too old to have more children, but it is still wrong. None of them are sex offenders, they are only hurting each other, but it should stop. If he doesn't realize it, he needs serious help.