I do not know, but I have the impression that Tachi can not touch Chihaya´s heart. She cares for him and he is a close friend. And it is undeniable that she was happy to revisit Tachi. http://mangafox.me/manga/chihayafuru/v02/c007/14.html  But it fails to thrill her. 

http://mangafox.me/manga/chihayafuru/v02/c009/18.html

http://mangafox.me/manga/chihayafuru/v02/c009/19.html