At the end of chapter 15, we learn that Siesta never stopped waiting for Shirou after the battle of Saxe-Gotha. Now that's love.
Because no matter how long it was, Siesta was patient. With absolute faith, the maid continued to wait. No matter what anyone said, be they commoner of noble, the country girl would not be swayed from her unshakable certainty that Shirou was okay, and that he would be back.
Enters Tear Jerker territory when you realize that Shirou will never return her feelings.
At the end of the Battle of Saxe-Gotha, Shirou dies... temporarily. For a moment, he sees Saber waiting for him in the fields of Avalon. But he cannot reach her, due to the fact he is currently being brought back to life. His thoughts?
Even if it was only a glimpse, It was enough.
She was still waiting for him.
And he was still searching for her.
Louise's internal monologue at end of chapter 16, that is all.
This, as well, enters Tear Jerker territory, since Louise is referring to Shirou's death.
After Louise uses her 'Absolute Command' in Chapter 20, pretty much the rest of the entire chapter is this.
Louise, as she watches Shirou's fight in chapter 22, even as she realizes that Shirou has always kept his tomb, Unlimited Blade Works, with him, she was determined to not let his vision of the future of him dying alone, come true, no matter if he lived or died, she was going to be there for him at the end.