What do you mean by, 'sometimes Neko went with her, sometimes he didn't'? Is it quite easy for you to transport pets back and forth?
My daughter (Chauncey) first moved to the UK about 10 years ago to work. She adopted Neko in the UK. Chauncey moved back to Canada a while later, and she brought Neko with her. Bringing Neko back to Canada was simple. She just had to prove (letter from vet) that he was up to date on all his shots. He travelled on the same plane as her in pet cargo (pets aren't allowed in the cabin on international flights, at least not on Air Canada). But he travelled well and didn't seem upset by the experience.
Then Chauncey decided to go back to school and she enrolled in Oxford to do her Master's. When she moved back that time, she couldn't take Neko with her, since moving to the UK was more difficult than moving to Canada. When going back to the UK, Neko had to have special shots and he was required to have these shots at least 6 months before he entered the UK. Chauncey hadn't known about the six-month waiting period (she assumed the rules to go to the UK would be the same as the rules to come to Canada). So, she had to leave Neko behind with her then boyfriend/now husband (Laird). Laird and Neko joined her about 8 months later. Again, Neko travelled in pet cargo and didn't seem bothered by it. However, Neko is a very laid-back, easy going fellow (Neko is the cat in my avatar).
Chauncey is still in Oxford, completing her PhD (I'm a proud Mom
). She and Laird have been back and forth for short stays, but they leave Neko in the UK. If they ever come back permanently or for more than a few months, they will bring Neko with them.
As for how difficult it would be to travel with a cat from SE Asia, you'll need to check into the rules, since the rules differ from country to country (and they differ depending on whether you're coming or going!). I think the more difficult aspect is finding accommodation in the UK if you have a pet...although perhaps some of our UK members will have tips on that.