EDIT: I've done my typical thing of quickly reading an OP and nothing else. I'm so sorry. I'm going to leave my post on regardless though, as someone else may find it rings true with their situation and manages to get the help they need. Sorry again and all the best to you OP!
I know everyone is saying he's controlling etc but I've actually been on the other side of this. When my mental health was bad, whenever my partner was away I had all sorts in my head. It wasn't that I didn't trust him as such, more that I didn't really know why he was with me as I didn't think I deserved him, or was worth much at all. So I was always checking he loved me, asking questions, looking over his shoulder if he was texting because I was always expecting the worst. Not just in my relationship, but in every aspect of life.
I have since got help with my mental health and I'm so chilled (with the same partner!) it's unreal. He can go out without me feeling anxious, I haven't looked at his phone in years, I don't need reassurance that he loves me.
Yes, my behaviour was terrible. But it was due to very poor mental health, which I then addressed. I couldn't help feeling that way at the time, and the way I felt seemed completely and utterly valid at that point.
If you've not been together long you may want to walk away, as a partner with poor mental health is HARD work.
But I would urge you to at least have a chat to him about maybe getting some help, as he shouldn't be feeling like this about you going away.
Of course, there is always the chance he's just a controlling bastard, but none of us know. I just wanted to put this side of things across.