It's also scary to think that I don't have control over this
You do have control over it, but it's just a matter of harnessing it.
DH travels a lot for work - always has.
I went through a period where I was feeling a bit low and insecure, and suddenly that seemed to manifest in being unhappy when he went away.
He goes away for conferences and meetings, and his company have away days (over a few days) every quarter.
He has never, not once given me cause for worry, so where this bout of insecurity came from, I don't know.
But, like you, I really did not enjoy the feelings I went through.
DH and I have been together many years now, so the logical part of my brain knew I was being irrational. Especially as we went through many years of it not being an issue at all.
If it helps to feel like you have some control over it, maybe think of it like this.
You always have a choice about how you react to something. That lies with you, and no-one else. Yes, there may be an initial visceral reaction, but you do get to choose whether you give in to that - or make a better choice.
He is going to go away. That isn't going to change.
So he can either go away under a cloud, with both of you feeling miserable, and with you feeling awful, and unhappy when he's away. Or, you can somehow take a deep breath, and just say goodbye.
You don't need to be delighted about it. That's a step too far. Just aim for being neutral about it.
He is going to go. He is going to be away. And then he is going to come home. And you do actually get to choose how you are when those things happen.
Practice this a few times. He already 'proves himself' by being trustworthy. Allow him to keep doing that. The more he does it, the easier this will become over time.
The choice is with you, you just don't feel as if you can exercise it. But you can, if you choose to. 
And as time passes, it will start to feel easier more naturally.