should I be worried ?

Me and my boyfriend have been together for almost 2years and the other day noticed that he has been talking to these others girls I don't think it's anything too bad but when we are together he deletes the messages. He thinks I don't know about it . Since he is hinding it from me do you think he is cheating or ?? And he has cheated on me in the past and we worked it out . Could he be doing it again??