A small recorder. If I start to "write" it then I want to "finish it" or "edit it" or something. A quick verbal note to self works for me.
It is like Tech said. It is all about communication and understanding. There must be agreement up front about what the relationship is all about. Friends with benefits? Just dating to see where it goes? No sex until I get a commitment of some kind? (not likely but....) This is a "writers' site" so shouldn't there be an emphasis on communication?
This relates very much to another thread = foreplay ie, FOREPLAY !! It is all about desire, readiness, passion.............yeah, and lots of lub.