Is he lying? should i worry? give me advice please!?

ok so when my boyfriend was over i was trying to get a wallpaper for my fone from an app on his and after i saved it to his pictures, i went to go send it to my fone and when i got to his pictures he immediately pushed end and i cud tell he was thinking of an excuse and he showed me some random video . im not sure if he was lying or not but what should i do? do u think hes lying? should i worry? give me advice please!!!