Why does Jesse feel lonely in the book Bridge to Terabithia?

Jesse is afraid of slipping off the rope and drowning ALL BECAUSE HE IS SCARED THAT HE DOES NOT KNOW how to swim

THE MAIN answer: Jesse does not know how to swim and he is scared if he slips off the rope while he is entering Terabithia and drown because it has been raining all month, too much water,and u need to swing across a rope to enter his and Leslie's castle which is Terabithia