US citizen married to UK citizen- file as single or MFS?

-I'm a US citizen
-My husband is a UK citizen employed by an American company in their London office, and hasn't made any money in the US, and only goes with me on vacation when I visit my mother, and a couple business trips to the company's US HQ
-I moved to London in January 2016, and have filed US taxes as required every year
-I've always filed as single with no problems
-Even without any deductions, our combined incomes (while enough to make us comfortable), wouldn't be enough to put us over the $105k level where we'd have to pay US taxes.

When I used TurboTax the first time I had to file taxes from the UK, I discovered my husband had to have a TIN, so I just filed as single and the return was accepted no problem by the IRS. But yesterday I got to googling and discovered belatedly that I have to file at least as MFS (would fit us best).

So I'm using the IRS online tool to see if my husband is eligible for a TIN, and nothing seems to fit our situation. Did the rules change? Anybody have any ideas what I should do?

You are married filing single.  Turbo tax doesn’t work for your scenario.  You’ll need to print the returns and write in NRA for your spouse. Alternatively, Tax Act does work in this circumstance.

You have been filing under penalty of perjury every year saying you are Single when you are not. I would look into filing amended tax returns as soon as possible.