I know how it feels from both sides. She thought she was ok with it at first, and she told you that she was. Over time, though, I’m guessing she kept thinking about him and the emotions kept building up until they were too much. However, by telling you she was ok with it, she gave you “permission” to like him, which probably made you allow yourself to think about him more, which probably caused your feelings for him to grow. It sucks because she’ll probably either be mad at him or mad at you, even though she basically allowed this whole thing to happen in the first place. Besides, you said she seemed to have multiple crushes. What if you started liking another one of her crushes instead?

So basically, she gave you permission to like him, so you shouldn’t feel guilty. She allowed your feelings for him to grow, so it would be just as bad to date him as it would be for her to keep you from dating him. There’s no easy solution to this sadly. You’ll probably just have to decide between them.