What should i txt this gir? 10 pts?

so this girl i really like or liked i took her to prom last week and we had a good time. before that we where kinda drifting away and i found out some stuff that really pissed me off she was taking and doing behind my back. not nessesarly bad but just kinda bugged me. i said to my bestfriend that after prom id drop her and go on my way and find someone els. So the monday after prom weekend, i went on my way and it was very heart sick to me to forget about her and not even txt her nor talk to her. i found out that she started to not like me anymore and started to like one of my other bestfriends. its been a week today since prom and i have just got a txt from her saying "she is slightly concerned that she hasnt talked to me for awhile" anywase, i dont know what to do or say. i kinda do have feelings for her still but im not sure if i should. i dont know if i should txt her now or wait till tomorrow. let me know what i should txt her. should i kinda be on the down kinda madish side or just keep it chill like where friends talking. im still alittle mad at her for going for my friend. please please help me on what i should txt her and also when. thank you so much 10 pts to best answer!!! i promise!!!