How would you react to the following couples scenario? ?

Partner B should ure A that they have no intention of being with someone else. B should then talk to their sibling to see if they did and then advise them anyway, to stay out of AB relationship. B should also advise the sibling that if anything happens to A, B will never forgive them and kick them out of their life. B should then turn down any attempt made by family members to see other people.