I think that Satoru said that he's interested in Yuka because he feels that Haruomi has feelings for her and wants to make him jealous of another guy hanging all over Yuka, thus him realizing her has feelings for Yuka and would want to make her be his only girlfriend and he can be happy. Because Satoru just wants Haruomi to be happy and he thinks that obviously the school nurse and Haruomi will be never be a thing, but thinks that Yuka&Haruomi would be better.