im rephrasing my dating question !!!!

i have been GOING OUT with this guy for two years and my bestfriend(not any more)gave him her sisters number to get back at me for an argument we had previous to this! now he kept telling me that he deleted her number and that he didnt talk to her but she kept calling me to tell me he was talking to her now ! so i brought this to his attention and he denied it but i had my sister go thru his fone recently and she saw the number and a convo between them !!! so what should i do !!!