Complex sentence: Joe's love interest working at the lunch counter was a woman of Greek heritage, which was written in mind for Peri Gilpin, however Gilpin was unable to commit to the role; thus the new character of Helen was created for Bernard.
Split into simpler sentences: Joe's love interest working at the lunch counter was a woman of Greek heritage. However Gilpin was unable to commit to the role, and thus the new character of Helen was created for Bernard.