Answer: Based on your description I am not certain what is happening, however it might be due to under or overwatering or it might be an insect problem. Geraniums should be watered when the soil has begun to dry out, it should not be kept saturated or sopping wet. When you water make sure the water soaks into the soil mix.
Check the leaves (especially the undersides) for signs of fine webbing, if you find this it is infested with spider mites which can be treated with a commercially formulated insecticidal soap. Read and follow the label directions.
I should also mention that geraniums need lots of direct sun to stay healthy and keep blooming. A north facing window will not be bright enough to keep this plant happy in the long run. You might consider moving it to a southern window at least during the shorter days of fall, winter and spring.
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