I bought my first flat with a workmate as it was the only way we could afford to get on the property ladder (we weren't poofters

). As we were moving our stuff in I discovered just how much of a prat he was. He obviously thought the same of me

'cos he moved out within a year and bought his own place due to a massive help from his parents.
I'd never buy a property again with anybody. Either 100% myself or not at all. Buying in a foreign land miles away will only add to your problems.
You don't seem to have any definite timescales e.g. ''I'm retiring in 3 years time''. Sounds like a bit of a pipedream to me and personally speaking, until you have retired and spent a few months in Thailand, I think it would be best left as that.
Who will look after the place whilst you are not there? How many months a year will it be used by you and your friend? What if you both want to be there at Christmas time? etc. etc.