never telling her sensei is him yeah (as per what he said earlier), and lying for now that "just being around the one I like makes me happy", as if he was satisfied with just that (which is also a lie as he says)
he's going to uphold the lies, presumably because he maybe perceives that to be a way for him to eventually have a chance again as "himself" once "Kiriyama" is out of the picture
maybe you're just joking, but it makes a lot of sense actually
"boy who cried wolf" is an old tale about a boy who kept lying to fellow villagers that he saw a wolf, until when there one time actually was a wolf, no one believed him anymore, with catastrophic results
in here, him calling her the Wolf-senpai is that same "cry" (lie) about the wolf (as he already knows her to be a lot more than just the "cold and indifferent wolf"), but he's going to keep calling it as part of the lie he otherwise upholds