Nope.. You're American.. Just tell them all you're an American. It gets you 15% discount on everything across Asia cause America saved Vietnam all those years back.. The Thais get you mixed up with Europeans though so make sure you keep telling people you're American...
The trick is to get the other 9 falangs to pay for you to spend time with her.. If she loved you she'd do that for you... That's the only way you can find out If you're the one....
I'd not be purchasing anything in Thailand... Buy something in your home country and rent that out and use the rent money to rent in Thailand... Spend 1 month in Thailand. 1 month in an adjacent country and keep alternating... They won't question that. Its the looking like you live in Thailand is what they don't want.