What does this mean?

Not sure how much back story is needed her but I'll give some context. Married for 20 years, three kids 10-15, both faithful as far as I know. I guess for the last year I've noticed that im the only one who initiates sex any more. It may have gone on longer but I either didnt notice or since I have poor memory just don't recall it.

So for the past 3 months my advances have been rejected, either being too tired or time of the month. She works and is a mom so I understand all of that, so honestly not reading much into it. So tonight she worked, I made effort that we had time to talk and listen to her day, affectionate kiss and touch after dinner, nothing unusual. Then around 8:30 she decides to go to bed. Family just watching TV at that point. Again pretty normal. I follow her to the stairs and whisper "hey I might be waking you up later..." she smiles and says ok. Im excited she maybe excited to see me in an hour when kids go to their room since it's been 2 weeks since we last had sex and her cycle ended on the weekend 4 days ago.

So later comes. I climb into bed. Move behind her. Wake her up with some hand stuff. Seems she's into it. Then it progresses with me behind her. Going at it for 5mins maybe 10, not looking at clock. I'm doing most the work but she's moving and seemigly into it (both staying quite which is typical when not alone in the house) then i move to position on top. But as I move she leaps out of bed and runs to the bathroom. Doesn't say anything. I hear the fan come on and she's there 3 minutes maybe. Im lying in bed waiting. Got visions of how fun finishing with her will be. When she comes back out she pulls pj's back on, pulls covers over herself, puts night mask on, and says "im just too tired " and turns her back to me. I'm left there lying on my back alone. I have no idea what this means.

She mad. She tired? Maybe she doesn't like what I'm doing down there? She doesnt have work tomorrow or need to get up early. 20 years we've never stopped without at least one of us finishing (usually both but im sure numbers are in my favor as a man). Can anyone relate? Any women able to place themselves in that situation and rationalize it? Im writing from the couch after I left her in the bed. Im beyond sad, angry, scared and probably a few other emotions I can't quite name.