The experiences and knowledge Jonas is gaining as a result of his training as Receiver of Memory has driven a wedge between himself and his friends. Jonas is changing in ways that they cannot understand. People in the community are carefully raised to be the same, and they are sheltered from feelings and events that might make them rebel against the carefully structured controls of their society. Through the lessons of the Giver, Jonas has experienced the depth of emotions and sensations such as love, desire, and pain; elements which are systematically denied the regular citizens. Because he now has the memory of these things, he can understand the horror and pathos behind phenomena such as war. His friends, who that very day had played a game of war and had gotten angry when Jonas had pleaded with them to stop, have no such perception of what these concepts really mean.
As Fiona and Asher ride off, Jonas knows he will be forever separate from them. He remembers sharing good times with them, but he knows "that such times had been taken from him now". He experiences an "overwhelm(ing) feeling of loss...he felt such love for Asher and for Fiona, but they could not feel it back, without the memories" (Chapter 17).
The euphemism for death in Jonas's community is "Release". Those who are released are believed to enter into "Elsewhere", an undefined state with positive connotations.
When Fiona and Asher rode off on their bikes Jonas felt alone because know one knew what he was going through and he wasn't able to discuss it with anyone, and he felt powerless because he couldn't have anyone else understand what he is going through.
biggy in the little hibby
ya u dunno me