It was confirmed in an Erin Hunter chat that Cinderpelt was in fact in love with Firestar. This was hinted many times, particularly in Twilight, when Leafpool is talking to Cinderpelt about Crowfeather. Leafpool says, "You wouldn't understand! You've never loved any cat! You've never wanted anything else!" Cinderpelt snarls at her apprentice, saying, "How do you know what I wanted?", hinting that she was once in love. Unfortunately, Firestar never realized.It is also noticed that Littlecloud and Cinderpelt seem very close as it is mentioned thathe sed to wait for her to go to the moonpool!