1m USD is a lot of money, but not enough to never work again - at least if we are not already old.
Personally I would do the same as always with gradual changes. I.e. go more often to good restaurants, buy some more tools, maybe a new bike, etc.
And for the gf: If she doesn't know about it, don't tell her. If she knows a lot of money is coming, give her what she thinks is "a lot of money", maybe 100,000 THB.