Marie, I remember (vaguely now as it was 35 years ago) something similar after my DM died (and that was not a good death: she was comparatively young, and she'd been ill and in pain for several years). For the first few months, I thought of her the second I woke up; gradually that moved further into the day - sometimes it was still first thing, sometimes it was mid-afternoon. Sometimes it was still many times a day.
Then the days came when, like you, I'd suddenly realise that I'd got to the evening before thinking of her. I still think of her most days, but usually she's just a presence - never quite not there, IYSWIM.
And grief never completely goes. It's that ball in the box analogy again - sometimes that small, hard, cold ball hits the side of the box and it just hurts so badly.
It is indeed a hard road, and it just carries on and on. But it does, very slowly, become on the whole an easier road, though sometimes there are some really horrible bits to work through. It's different for everyone, too. About the only positive thing about it is that you learn the measure of your own strength.