@jezza I know everyone is attacking him ... there is a but though
Less than a month ago, he sustained a concussion. It takes years to heal from one. The more active you are in the initial post-concusaion phase, the longer it takes.
For your relationship and his health to thrive, somethings gotta give. I agree with him not going on the trip. Concussions really impact mood, like you don't feel quite right... so that explains why he just abruptly said he wasn't going. His ability to reason isn't as strong as it usually is. I think he should defer his masters program too. I say that as someone who received 2 concussions within a month of each other and then went on to do a very intense undergrad. It was horrible and if I could go back in time, I would take a year off to heal. It took me 7 years before I felt normal again and I'll always wonder how different things would have been if I slowed down.
If I were in your shoes, I would be so let down and upset. How dare he drop this on you the day before you leave! ...but given my own healing post-concussion, I have a little empathy. Going on the flight would be so hard on him and may delay healing in the long run. He would be more of a burden. At home, sleeping, is what he should be doing. He has the opportunity to be undisturbed for a few days and I encourage it. You'll be surrounded by your entire family.
Edit to add: (I'm breastfeeding so now I'm sitting and snooping through past posts) ... yeah OP, I see where you're coming from now after reading your post about a certain ex. I'm sorry.