I feel really sad, confused and like i wanna cry?

so basically im a 15 year old boy, my best friend (a girl) who i secretly like just revealed that she self harmed once a few years ago and i feel reaaallllyyy bad about it even though shes the one who brought the subject up :/ i talked to her after about how i once felt suicidal and she was really shocked. i dunno why i feel really guilty about her self harming though, i feel like i should have been able to do something about it :'(