Op, have you ever had a woman really into you? Many haven't so don't know the difference. was she really into you in Thailand? Signs, always picked up your calls, always ready to meet. Would blow off other engagements to be with you. Never made you wonder what she was up to etc
If yes she was into you in Thailand then I'd lean towards depression. Which can be helped.
If she just was never that into you I'd lean towards her just realising that being with a guy just to be able to work in the UK feels like a prison sentence.