Q.why are the flowers on my tomato plant disappearing
One day I will have flowers on my tomato plant, and the next day it looks like someone cut them off.

Certified GKH Gardening Expert
It is likely a pollination problem. If the flowers are not pollinated, they will simply fall off to the ground and the flower bracts will look like someone snipped them off. These articles will help:
https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm
https://www.gardeningknowhow.com/garden-how-to/beneficial/creating-a-pollinator-garden.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/pollinate-tomatoes.htm
There is a slight chance that it could be rodents eating the flowers. This article will help with that:
https://www.gardeningknowhow.com/plant-problems/pests/animals/garden-mouse-control.htm