You are free to choose forgiveness in this case. Even though your son’s ex-spouse did not hurt you directly, she did hurt you in a secondary sense in that she hurt your loved one. Forgiving in this context is appropriate. You are not being disloyal to your son if you choose to forgive to rid yourself of resentment. You need not, then, go to your son and proclaim your forgiveness and then pressure him now to do the same. You can forgive without discussing this with your son. If and when he is ready to forgive, then you can share your insights about the forgiveness process with him.
Learn more at 8 Reasons to Forgive.