What comes first erosion weathering or deposition, or do they happen at the same time?

Weathering would come first then erosion then deposition. Hope that helped a little bit. And no none of them would happen at the same time i would believe thats impossible.

Let m help you
Weathering, Erosion, & Deposition:
These 3 work together in a continuous cycle that BOTH wears down & builds up Earth`s surface. 
-Forces that build up Earth`s surface are called constructive forces.
-Forces that tear/wear down Earth`s surfaces are called destructive forces.
-Sometimes erosion & deposition work slowly, other times like in a thunderstorm or a flood they work quickly. 
- These 3 are NEVER ENDING! 
Have a good one!