What are my visa options for retiring in Thailand without being married?

There are actually 3 options you have;

-go get a 90 day single entry Non-O visa either in the US or from a thai consulate in a neighboring country

-go to the immigration office and apply for a 90 day Non-O visa (having at least 15 days left on your current admitted until stamp

once you come back into thailand on those you'd be stamped in for 90 days Getting the Non-O inside or outside the country would require you meeting the financials of either banking 800K baht in a thai bank, or getting the notary affidavit of income letter from your consulate stating you get 65K baht a month in income.

Then you can apply for a yearly extension of stay based on being over 50 (retirement) at the immigration office again, by meeting the financial requirements.

OR you could

-go back to the US and apply for a year-long, multi-entry Non-Immigrant Type O-A (Long Stay) visa from either Chicago, New York, LA, or Washington DC.

That visa does require a police background check a medical certificate and financial proof (but you can bank the money in the US) It would get you stamped into thailand for a year at a time every time you enter the country for the validity of the visa itself.

Those are your options ;)