I found myself in a similar situation but I am the guy and the girl was moving away. I was with her for even less time than you guys and I really wanted to move with her. In a short time we had spent a lot of time together seeing each other up to 5 days a week and did the same sports together and things were awesome etc.

My reason was simple in that I wanted to be with her forever (unlike this guy I did not say that as no one can tell what will happen...) and was willing to take a chance.

She was not moving halfway across the world though, but a days drive up country so it would be a lot easier to join her. I already work remotely so all I needed was a place to stay.

When I proposed the idea it did not go well and she also said that she was "freaking out". I was amenable to any solution, such as flying up once a month to visit her etc. and not just wham, bang I am there full time at once, but she was amenable to none. A few weeks later I can conclude it is a good thing as we had no future together given she didn't even say I could come visit and various other reasons that I turned a blind eye as I was infatuated with her.

So my advice would be: a - realise he is infatuated (as he said he wants to be with you forever), which will affect his decision making for the worse. b - think long and hard do you actually have a future with him c - if yes, start small, rather see if he can work remotely and he visits you for 2 weeks at a time or something rather than have to commit with leases etc, changing jobs, and really move your cheese, i.e. minimise any fallout blowback