Is my boyfriend cheating or am i over reacting?

okay so when i asked my boyfriend if hes ever cheated and like keep asking cas i think he has cas of da messages i found from dis girl and den da text messages and he claims he neva hung out wit them so idk wad to believe..ughh is he lying or tellin da truth yu think.. i mean im with him on weekends n he always calls me so how cood he cheat ??