What happens to Albert and his friend in the trenches

I'm not sure what you are looking for in particular but I do know they had the futile job of facing an enemy with machine guns.

We don't read about Albert in trenches, we know that he"came all the way to France just to look for him (Joey)" - chapter 21. He joined the Army when he came of age to look for his horse and we find him working in the veterinary hospital behind the front line. On the other hand, Joey knows everything about trenches and "no man's land" since it is a war horse used in battlefield. (see chapter 6 - Joey's first charge ). Albert and Joey were never together in trenches.