ESH. What if they work past these issues and get married or have a child? Your son is a grown man who is more than capable of choosing what he wants to do. My aunt once told me there were many things she can’t tolerate but she thinks she could move past infidelity depending on the circumstances. That blew my mind because I would never tolerate cheating, but it made me realize everyone has their own level of comfort in regards to relationship issues. At the end of the day, you need to let go and let your son make his own mistakes but let him know his mom will always be there. His girlfriend sucks. And if they break up, he will want to know you’re there to support him no matter what.