He can't break it? She keeps his comment of 'tricky' in mind for later but she's fine for now. What he said is what she needed to hear from him in regards to this arrangement

"That's all I needed to know. I think I should leave you be now. Wouldn't want you to have to make another deal with someone." Thank you very much, Steffi. That's one form of guarantee for Aradia's safety in the future.