My friends think i am ignoring them. What should i do?

I n my best friend r really close…v r best friends since bout 8mnths..my old good friends think m ignorin them by being wid her in recess etc…well I have one and only best friend firs time in my life and we both really enjoy having fun together…I like spending time with her more than anyone else...I try to spend time with my old friends whenever I can and m not ignoring them….but I can’t give them as much time as I used to……what should I do?