Every day is exactly the same at Sir Leoline's castle. No matter what good things happen or what bad things happen, nothing will ever change. Since change is inevitable, and only change can create growth, Sir Leoline's world is stifled and dying. Maybe this is what made the castle's protective forces weak enough to let Geraldine in. Perhaps in some ways we can see Geraldine as a savior figure, because she's there to shake things up.
Save the boss of the shield of Sir Leoline tall, Which hung in a murky old niche in the wall. (162-163)
Sir Leoline was clearly once a warrior knight, but now the tools of that trade are hung up in a wall niche as decoration.
And will your mother pity me, Who am a maiden most forlorn? Christabel answered—Woe is me! She died the hour that I was born. I have heard the grey-haired friar tell How on her death-bed she did say, That she should hear the castle-bell Strike twelve upon my wedding-day. O mother dear! that thou wert here! (194-203)
No one in this poem can stop talking about Christabel's poor dead mother. Get over it, folks.
Each matin bell, the Baron saith, Knells us back to a world of death. These words Sir Leoline first said, When he rose and found his lady dead: These words Sir Leoline will say Many a morn to his dying day!
And hence the custom and law began That still at dawn the sacristan, Who duly pulls the heavy bell, Five and forty beads must tell Between each stroke—a warning knell, Which not a soul can choose but hear From Bratha Head to Wyndermere. (332-344)
We're guessing that there aren't too many immigrants to Sir Leoline's lands, and the ones who stick around are either early risers or they're partially deaf and can sleep through the daily cacophony of bells.
But when he heard the lady's tale, And when she told her father's name, Why waxed Sir Leoline so pale, Murmuring o'er the name again, Lord Roland de Vaux of Tryermaine? Alas! they had been friends in youth; But whispering tongues can poison truth; And constancy lives in realms above; And life is thorny; and youth is vain; And to be wroth with one we love Doth work like madness in the brain. And thus it chanced, as I divine, With Roland and Sir Leoline. Each spake words of high disdain And insult to his heart's best brother: They parted—ne'er to meet again! But never either found another To free the hollow heart from paining— They stood aloof, the scars remaining, Like cliffs which had been rent asunder; A dreary sea now flows between;— But neither heat, nor frost, nor thunder, Shall wholly do away, I ween, The marks of that which once hath been. (403-426)
Sir Leoline just can't get over anything it seems. He wakes up every day with a reminder of his dead wife, and he apparently can hold an Olympic-sized grudge against even his best friend. We can only hope that the planned-for end of the story had Leoline moving on in some way or another.