I told my girlfriend that I have feelings for my ex?

she began crying, and said that if i needed a break from our relationship to sort things out she'd let me. however i felt way too bad that she was crying to accept that offer. so now were still dating, and things have gone back to normal. now that ive told her this my feelings for my ex have diminished but i know theyll come back. my girlfriend began talking and flirting with me right, and im talking like immediatly after me and my ex broke up. so i guess she couldve expected it but i dont know. what should i do?