"同事和我老板的心腹互相看著不順眼才是問題的關鍵"

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.