Who is Leo Kovalensky from We the Living and what is their importance?

Kira meets Leo on the street after having an argument with Victor. She presents herself as a prostitute, and Leo admits to being tempted, but also makes it clear that he doesn't pay for sex. Kira falls madly in love with Leo, but he never seems to have the same passion for her..... note, he does love Kira. In the end, Leo leaves Petrograd with another woman.