I have two close friends who were constantly mistaken for a couple. Guess what happened? When asking me for advice, the female friend expressed this worry. In this case, I'm guessing it came from watching too much television, because I'm convinced that the idea of failed romance ruining friendship is a an extreme Logic Failure.

Oh, no, it definitely happens. And one friend expressing an interest that turns out ''not'' to be reciprocated is even more likely to ruin the friendship. Though as always it depends on the people involved.

... this is exactly why this troper doesn't want to tell her friend about the crush she has on him.

This troper has been (and currently is) on the receiving end of this. For his part, he at least has the honesty to say "I'm just not attracted to you" if he's not interested in his friend's advances. This is a rare occurance, however.

Back a couple of years ago, I realized I liked my best friend. I was afraid of telling her about my feelings, because I was afraid of this trope (and she had previously had a friend who also told her his feelings, that she didn't reciprocate, and she felt bad about it). Eventually, not only I told her and realized she also felt something about me (she even said it was obvious she HAD a crush on me, even some of our friends shipped us), but we also broke up, and we still are good friends after that.

This troper subverted CannotSpitItOut and got pretty much this back. I'm not sure if I'm just thinking wishfully, but I suspect she'll warm up to the idea over time. Here's hoping.

Said verbatim by this troper to his best friend. Two weeks later she got together with this troper's other best friend and broke up with him after this troper moved. Ironically, I lost both of them over this.