Complex sentence: Mugi's childhood friend who has been in love with him after someone told her that she with Mugi looked that of a "prince" and "princess" and has been trying to act and look like one ever since.
Split into simpler sentences: Mugi's childhood friend who has been in love with him. After someone told her that she and Mugi looked like a "prince" and "princess", she had been trying to act and look like one ever since.