Am I pressuring him to move in?

We've been dating for over 3 years. We have both shared the same attitude about living together, and it happening when it happens. We have never felt the need to rush anything. And so, in the last few months we have been feeling the desire to take a step and move in together, and it has caused a lot of miscommunication and frustration. I am ready, and taking all the necessary steps to progress this, however my partner is having cold feet suddenly. I have no doubt that he loves me and want to be with me, but I have no idea why he is apprehensive to take this step. We are going on 4 years together and I'm 27 and he's 26. Any comment?