You are dealing with a lot of emotions about your relationship and it must be really difficult to be doing that without support.
What brings you to believe it's specifically separation anxiety? Did you feel the same way when he'd leave before the new job? I'm not saying it isn't, but it sparks my curiosity about what that means to you. It definitely sounds like you are grieving a pretty significant change in a relationship that you are invested in and a change in a person that you love. That's so tough.
Another thing to remember is that no matter what it looks like, you are coping in some way. Rumination and worry are both ways of coping. Crying or retreating from the world is also coping. What do you want your coping to look like? Most people want their coping mechanisms to reduce their uncomfortable feelings, so separating what meets that need vs what doesn't can clue you in to what will work best for you. It doesn't necessarily mean you always have to escape your feelings though. It's OK to feel everything you are feeling because you're human and you care.
It's also worth noting that his actions (or lack of) are triggering these feelings you have about you. I don't know enough to speak to where that comes from for you, but how much of what he's choosing or not choosing to do is possibly about him? When we don't know why someone has changed their behavior toward us, we typically end up blaming ourselves because our brains don't like uncertainty. The truth could be much different. The only way to truly know is to express that to him--though that is up to you if you feel like you are in a position to speak your truth to him.
Support from other people in your life could help as well. Maybe someone outside of the relationship can give some unbiased suggestions or even just offer support to you while you are moving through this really rough situation.
One way to look at how you are feeling is that your emotions could be reflective of what you want for your relationship vs what is happening now. If there is some separation anxiety, maybe that's something that warrants more inner work for you if you so choose. But it's normal in any relationship to feel upset when our partners aren't meeting our needs. You probably know best which scenario fits your situation, and maybe it's a little bit of both!
If you decide to confront him, speaking with someone you trust to help you with that or seeing a counselor could help to narrow down what you really want him to know and what you need from him.
I wish you all the best!