As much as you don't want to contemplate it, he could have met someone who he quite fancies and wants to try it out, hence the sudden 'not wanting to committ' after 4 1/2 years. He wants to dip his toe in the water, so to speak.
It could be a blip but you need to hear the alarm bells and protect yourself,,,,and your heart. You need to ask him to move back to his parents and you need to think what you want to do, it's not all about him.
If he truly loves you, then it will work out and if he doesn't then it won't. Surely, you wouldn't want to be with someone who didn't truly love you.
Remember this..."Man will move heaven and earth to be with the woman he loves." Don't accept anything less. x