Brother and sister hood

Through a group on social random girl and me talked. First we both were willing to be best friends but after some time we both decided to be as brother and sister BC she doesn't have brother. And then we both attached to much to each other.we both have and had only Intention of a brother and sister no any other relation . But now we realised that maybe it is not allowed in islam being brother and sister by your own . And if it is not allowed so please give us a way through which we can talk BC we both are attached to eachother too much .