Clovie
A cycle, kept between the two of you
A private diary that only the two of you can see.
Periods, symptoms, mood and flow go in as they happen, and any month can be filled in late or put right. The forecast reads what was actually written down, so it gets better as the diary does.
It lives on your shared account and nowhere else. No advertising, no selling on, and the whole diary leaves with you if you delete the account. What it does with data is written plainly on the privacy page.
Whether it is shared at all is a choice. Tracking can be on for one person, both, or neither, and it is switched on the personal page, not buried.
Free, on Google Play. Android only, for now.