Is he lying to me?

So this happened last night. Oh course I feel like it my fault for being nosy but I can't help it. My boyfriend gave me his Kik password a while back. I got on it today. It was fine until a girl messaged him. I acted like him by not saying much. I told her I had a gf... Acting like him. She said " I know we talked about it before." And I got worried. I flipped out on my bf. I told him it was over because I can't be with anyone loyal and he cried for hours. He told me he found her on a game and need more players. I feel like he's lying. He changed his password and wouldn't let me talk to her. And this morning he gave me his new password and I can't find her on there. Help!!?