In the past, I was like you where I would keep going even though I felt fatigued. My motivation would go down and down... getting even more tired... and still I wouldn't deload. Just take a couple days off cause my motivation would hit zero.
Nowadays I listen to my body. I used to train 3 on 1 off, now I do 1 on 1 off. The difference? On the days I train, I have a lot more energy and a lot more motivation allowing me to have amazing sessions almost all the time.
Now when I get in the gym and I feel unusually tired, I tone it down and not push myself so hard. Doesn't mean I don't still get a good workout. But I stop myself before I exceed my recovery capacities and guess what? I've consistently been making progress for weeks. Months even. It's a lot more worthwhile to let your body recover well rather than having an extra day or two working out. You will stop growing eventually if you go balls to the wall all the time.
Just listen to your body and actually trust it. It's not just you when your motivation goes down - it's your body telling you something.
One of the best pieces of advice I ever got is this: when you train, a third of the time you will have normal workouts, a third of the time it will be not-so-great, and a third will be very good! It's those very good ones that will give you the most growth.