Boyfriend wants to move back in with his parents and won’t tell me why

All he says is “I’m moving back in with my mum as I don’t want to be here. “ that’s all.

What the hell why would he say this.

We have been together for 7 years. I thought our relationship was good and we were happy.

He’s not grown up enough to tell me why he wants to leave.

Imagine sleeping next to someone for 3 years straight and then them suddenly wanting to move out without no explanation and he wants to carry on our relationship. I don’t think it will work