Was she jelous of me and her friend?

so ths girl that did not fancey me was jelous i think what do u think bc me and her best friend was dating and she did not talk to me but before we started dating dating she was loving and lively around me but when me and her friend was dating she was not looking at me when me and her friend were kissing and went to bed early but whn me and her friend ended dating she was loving and lively around me again why but she has never said she has not fanceyed me and her name is lisa and her friends name is emma