Why do you think Leper signs the telegram he sends to Gene, "Your best friend"?

Leper is a loner. He is secure in his position as the odd one out which explains his earnestness to join the war. After the war, leeper has changed. He needs acceptance, he needs social peers. Leeper sees in Gene a potential confidant, a soul mate. Leeper knew how close Gene was to Finny and thought that perhaps he could take Finny's place hence the emphatic "best friend" at the end of the telegram.