"同事和我老板的心腹互相看着不顺眼才是问题的关键"

As you said here, this is the key. In this case, there is nothing you can do to change the situation. Your colleague needs to make significant effort himself to mend the relationship with boss and the boss' inner circle, under the condition that the boss is willing to give him the opportunity. otherwise, no one can help him. The best thing for him is to walk away. This is a lesson I learned.