what can i do?

I think you should tell him how you feel, and talk about it. Maybe you could visit him, and stuff. That's the only advice I have.

Maybe you should stop pretending that you're fine, when you're not. To me pretending sounds like a lot of work.

If there's no way you two can stay in touch, or get him not to go. Then you just have to deal with it. It's a little something I like to call "Reality".x

Good luck