IS HE A CHEATER?

What are the signs that your man is cheating? My man doesn't like to dance but all of a sudden, he has started going to clubs and when he is out with his friends most of the time he doesn't answer his phone.

And when he's around me, he never let's his phone ring, he keeps it on vibration. And he also keeps it locked every night, he says it's because I look through his messages all the time...what do you think?