In reality their attitude probably has more to do with the loss of their family and their mother’s insecurity that he has moved on, then it really has to do with his new love interest. In this case the adult children are displacing their hurt onto the wrong person.
2. Align With Your Girlfriend. A man’s children need to see that he is strong in his decisions. If he gives in he teaches them that getting upset in life is going to make things go their way. If adult children learn that all they have to do is get upset and threaten him and he will drop all his personal needs and desires to please or “keep” them, he is teaching them to have poor character. If he loves his girlfriend and aligns with her, they will follow suit. If they feel his insecurity, their hate for her will increase and she is left scapegoated and unprotected.
3. Empathize With the Adult Children: It is harder for men to move on after divorce then women because children tend to want their dad to themselves, and while this is understandable, divorced men deserve to be happy in their own lives just as they support their adult children to be happy in theirs. Not to allow this to happen is very selfish on their part. They are old enough to know better.
4. Empathize With your Girlfriend: Being the woman in this triangle is the hardest place to be. The woman needs to know that the man is unequivocally supportive of her and their relationship.