What do you think of this guy's behavior?

Hi, I'd like to ask for your interpretation on a guy's behavior. Please help me. A guy (1)seemed to be angered by another guy (2), and guy 1 kept trying to warn me about guy 2 and his deceptive behaviors behind my back. Guy 2 never said a word about his behaviors behind my back, and I learned about them through guy 2. They two actually haven't met each other but have exchanged e-mails, while I know both of them. Guy 1 seemed eager to find out how I feel about guy 2, and I basically answered all his questions about guy 2. Now he knows how I feel about guy 2 and has become less responsive to my last 2e-mails and IMs. I don't understand why guy 1 behaves in such a manner. What do you think? Could you please tell me how you think of guy 1's behaviors? I really appreciate your help.