Your partner isn't rejecting you. They're guessing
Here is the shape of it. You stop initiating, because it hurts, or because desire has gone somewhere you cannot find. They notice. They do not ask, because asking feels like pressure and they do not want to be that person. So they stop reaching for you.
You notice that. And you conclude that they have stopped wanting you.
Two people, both hurt, both silent, both entirely certain the other one left first.
Why nobody speaks
You do not raise it because you have no explanation you trust, and because you are quietly afraid the answer is that something in you is finished. They do not raise it because every version of the question sounds like a demand. Both of you are protecting the other from a conversation you are each convinced would go badly.
Meanwhile the silence keeps compounding, and silence is the one thing in a relationship that never stays neutral. It fills with whatever story each person was already telling themselves.
The thing you have that they don't
You have information. You know something is happening in your body. They do not, and in the absence of information, people do not conclude "her oestrogen is fluctuating." They conclude "she doesn't want me any more."
You do not owe anyone a performance of desire. But you do hold the only piece of the picture that can stop this, and handing it over costs less than the silence does.
What to actually say
Not in bed. Not after a refusal. Choose a neutral moment, a walk works well, and open with what is true:
"I want to talk about something I've found hard to say. My body is going through a hormonal transition and it's affecting my energy, my mood and my desire. It's not about you, and it's not about us. I'm getting help, and I need you on my team while I do."
Then say what would actually help. For most women, it is some version of: patience, and affection that does not have to lead anywhere.
If they take it badly
Some will, at first, because they have been quietly hurt for months. That is not a verdict on your relationship. It is the sound of relief arriving late and disguised as frustration. Give it a day.
Couples who face this together usually come out closer. The ones who do not are almost never the couples who had the hard conversation. They are the ones who kept waiting for it to fix itself.
The full Partner Conversation Toolkit is inside The Shift Method: scripts for you, and a guide written to be handed to them.
See The Shift MethodGeneral education, not therapy or medical advice.