The principle of eternal loyalty is not blind obedience to a cause or person without due consideration. Rather it is founded on trust or belief that one’s core values and ideals are shared by a given cause or person, and that the cause or person is worth being loyal to because of the fundamental characteristics of the cause or person, that should not change or deviate, but are permanent features so long as the cause or person continues to exist.
A cause is worthy of eternal loyalty if it is a morally good ideal, that is to say, if it is right to the best of your knowledge to pursue the goals of the cause. If such a cause is truly righteous, it should remain so for all of eternity. Thus your loyalty should be eternal.
A person is worthy of eternal loyalty if they are a morally noble and innocent person. That is to say, that their values and beliefs are consistent with what you believe to be morally true. If such a person is authentic, their nobility and innocence should be constant throughout their remaining life. As such your loyalty should be eternal.
The only time in which eternal loyalty should ever be broken is when the cause or person breaks your trust by proving to actually be morally false. This indicates that your judgment of the cause or person was mistaken, and as such requires that you end your loyalty because they do not actually deserve it.
Eternal loyalty then is conditional on a cause or person being honourable and justifying this loyalty.
Understand that people especially are fallible. To fail at maintaining one’s nobility or innocence at all times does not necessarily mean they are morally false. It simply means they are human. The more important consideration is whether they actually believe in what they strive to be and do, and if they actually try to live up to the standards that they value. So long as they earnestly strive for what is good and right, they can be considered noble, honourable, and innocent.
Eternal loyalty demands faith, because there will always be uncertainty about the truth of causes and people. There will always be a risk that you are wrong to place this faith in the causes and persons that you do. However, the value of eternal loyalty stems from the strength of the bond that unifies and aligns the cooperation of many allies that they can achieve far more together than they could alone.
Thus, eternal loyalty is a principle that should be upheld whenever possible. It demands a careful assessment of the character of others, and a strong faith in the truth of that assessment, because once made, it implies a commitment to that other that people should be able to depend on for strength.
Eternal loyalty however must not be blind to the deal breaker of dishonouring your loyalty by intentionally breaking your faith in them, or proving themselves to not be who you believed them to be. Then and only then, you are freed of your obligation to them, for they, and not you have broken the social contract of trust between you that is the foundation of your loyalty.