He got mad when I asked him if he is cheating on me!!!!

I suspect that my boyfriend is cheating. I heard rumors, he acted strange on the phone lately, has a password on his phone and he never has time for me. I asked him and he got REALLY REALLY MAD. I don't know how to deal with his reaction. I'm not good in human psychology, but what does this mean?
He got mad when I asked him if he is cheating on me!!!!
Post Opinion