Is she mad at me or am i reading into it?

my best friend of 13 years never IMs me anymore. whenever i im her she always IMs back but she doesnt say much. i ask if shes mad at me she says no. shes been really busy lately. she DOES have 2 jobs school and a boyfriend, but she did before and always IM'd me then... im not a stalkerbut i know she talks to her other friends through facebook anfd myspace and she never writes to me unless i write first. i tell her i still want to be friend she says "of course" i dont know what i did wrong. weve been friendsfor 13 years i dont want to lose the friendship if u can call it that. what do i do?