Omg..i feel really bad naow :( what shall i do? i lost my bestfriend?

hiya.. im 13.. the other day..me and my 'best friend' had an argument..and then the next day, we were friends again..(this happened about two or three times this week - i know. pathetic tbh.). And its got really bad naow :(.. we argue like every night.. and today has been the worst.. she wouldn't talk to me or anything. i lost my bestest friend because i went out with someone. secretly. buh now its just getting pathetic tbh. i dont know what to do anymore.