What is ual chemisty?? Can anyone explain this.?

As there is a guy and we have a connection and ual chemisty......we do kiss but I cannot go further as I am scared and I want to save it for the right time. But he stays away :( and this does hurt me, so I dont see him that much, seems like he only comes when it suits him and I feel that he is using me here.. :( Does he like me?