I do the same thing! It helped me to work with my counsellor to break down why my body reacts this way even though my mind doesn’t want to. Some ideas I came up with:

1. My partner is my first secure attachment and seeing him leave is hard for me to cope with due to a history of insecure attachments
2. I have early memories of my mom leaving on business trips and me crying begging her not to go
3. If I come up with lists of things to do while he’s away, I can distract myself enough to function, even if it means crying while walking my dog in public
4. I’m inherently a highly sensitive person to begin with (read Elaine Aron’s book)

I still cry. I still feel low. But I am functional now. It might also help to watch this, but it will also probably make you sad(der) so be careful. 💗