How to make my bf overcome his Shy on me?

How do i make him more comfortable around me? He really speak softly to other people except on his family he talk like normal. His sister said that he talk soft and gentle to other people he doesn't know and talk normal to the people he really close with, well me and him are pretty close when we go out why is he still speak softly to me and he's really gentle and always smiling.. When i ask for a kiss he kissed me on the cheek most of the time and seldom on the lips, never try tongue before... Any idea on how should i help him to overcome her shy on me?