Dont have proof to show him so he cant denied it anymore

I look on my bfs phone when he went to bathroom I found out the two days he came home late he was with a girl I got her # n call her she told she's bn seen my bf since I move in with him that is 9 months ago I confronted him n he denied it he still is I have proof to show him but he still trying to talk to her she told me he s bn texting her please advise I'm confused