That list of questions suggests "No" as the resounding answer.
If you want to protect your 'investment' do it with a Usufruct. In reality a waste of time - you have identified two keys factor; what is spent is spent and you have no intention of staying put in the event of her demise.
She could bequeath the house to you, giving you a year to transfer it toa Thai.......good luck with that one.
As an aside, if you do decide to marry, remember that marriage invalidates existing Wills; you would need a new one if, for example, there are assets and beneficiaries back home.