Question About Filing Singe Or Married

AskTaxGuru.com Junior Member, bulls2030, asked:

Hi,
I got married overseas and my spouse and child at the moment live abroad.
My spouse does not have a green card or anything and we are currently waiting for her immigration.
Well for my past two tax returns, I have been filing my taxes as married filing separately with my spouses name, but haven't got a TIN or whatever that is called.

I have been searching online for this issue if I can file my taxes as single because my spouse and child have not immigrated to the USA.

So I have two questions.

1) Based on my situation described above, can I file my taxes as "Single" or do I have to file as "Married Filing Separately"?
2) If I can file as single, will the IRS say something since I already filed my past two returns as married filing separately with my spouses name and none EIN or TIN or whatever that is called?

Anyone's help would be much appreciated
Thanks