Messy Rebound

My girlfriend & broke up recently. She really made a joke out of me so out of spite I hung out with a friend (a friend of hers too) and we kissed. I knew this other girl was emotionally vulnerable because she was also going through a rough patch with her ex and I purposely took advantage of that. After I dropped her off I called her & told her I was really sorry & it was wrong of me to do that. Everything is very normal now but she casually flirts with me hoping I reciprocate...and Im still hung up on my ex, we've been rebuilding our friendship.