We use 'at the end' for things that have natural endings. For example: At the end of the film/book/ course/ week/ year We use 'in the end' to mean 'eventually'. For example: When John first met Stephanie, he thought she was a nice girl. But in the end he realised that she was only interested in him for his money.

well, in the end = finally, or final outcome of something; at the end could be either a physical end or a metaphorical end. e.g: in the end: we tried really hard staying together, but in the end we broke up. at the end: at the end of the street. at the end of the story. I hope this helps.