I(24M) want to ask for a date to a girl (23F) who is in situationship with her boyfriend since a long time. What should I do and how should I proceed?

I(24M) want to ask for a date to a girl (23F) who is in situationship with her boyfriend since a long time. She also happens to be my good friend so does not want to ruin that as well. What should I do and how should I proceed?