Is it normal that he's scared to commit?

Me and my bf have been dating for quite a long time and for months he's been asking me to move in. It was a mutual agreement and after months of saying I'll move in, I actually did it.
I transferred my job, my parents bought a smaller house, we've been preparing it since around November.

3 days into living together he suddenly asked me to move out because he doesn't want to commit.
What does he mean?
Were in love, we get along great, I get on with his housemates. We've been happy about the decision the last few days and then he said it so suddenly.

He said at the start of the relationship he was scared to commit to us but after a while it went away.

Should I be worried? How can I understand what going on in his head?

Sorry for the long question.