Alfred's blind love for Sarah in general, whether she deserves it or not. Culminating in "Für Sarah", which can double as a Tearjerker, once you know, how it's going to end.
A small moment occurs in "Sie irren, Professor". While the Count mocks Professor Abronsius, Alfred, terrified, hides behind his mentor, who shields him from Von Krolock. Pet the Dog or Papa Wolf? You decide.
As funny as "Wenn Liebe in dir ist" is, there is something rather heartwarming about it (though it depends heavily on the actors portrayal). At first, Herbert seems to be flirting rather harmlessly with Alfred. The moment he caught sight of Alfred's book ("A Guide for Lovers") Herbert looks like he genuineley believes Alfred came barging into his bathroom because he loves him. Keeping that in mind, his confession about his feelings for Alfred seems genuine in it's own right. Which makes his incredulous look he sometimes sports, when Alfred claims he didn't do anything to "provoke" him a lot more understandable.