having trouble connecting to my boyfriends world in minecraft

I have been able to log into my boyfriends world several times but the past few days I have not been able to. It keeps telling met that I am unable to connect to his world. Even when he invites me to play. It does not tell me why I cant connect. 2 days ago it let me connect after about 2.5 hours of trying. There is nothing wrong with our network.