Why still lie?

so me and my now ex boyfriend has a really hard time in the end , then one day before we broke up i stoped by his flat to pick up a letter , i didn't tell him i was going to come , what i saw was that all my bathrom things i had there were packed and hidden in a bag at the bottem of the coverd and that all my close were hidden under his in the closet and there was a toth brush that wasn't his and wasn't mein and this is after a weekend where he screend me. i think he cheated on my but he still says no i dont understand why would he keep on with a lie now? since in my eyes all sings show someone was there and that someone was not suppose to see my things. sorry if my spelling is not perfect English is not my native toung