Another idea would be for both of you to mark the first day of your periods on a prominent calendar in your house... actually I think all women should do that.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
Mags, F, 60, poly-dating, loving and living with
miss pixi, F, 38
Punk, 41, M (dating since Oct 2015)
and a few more casual relationships