What should I do after my 90 days on a Non-O visa in Thailand?

Where did you get your Non-O visa from? Your country? Or from Thailand?

The first time, they issue visa for 3 months. And then you will have to renew your visa again upto 1 year duration from immigration office. When they renew it after 3 months, they usually renew upto 1 year. In that case, you will not have to go out and get stamped once you receive the 1 year non-O visa (single entry or multiple entries).

Example:

Suppose u got ur first Non-O marriage visa on 1-May-2018. You must renew it again before 1-Aug-2018.

Suppose, when u renew it on 30-July-2018, then your visa expiry date will be 1 year after that date on 28-July-2019.

In my case, that happened.

So as i understand it with the 60 day extension after the 15 months means you get 17 months out of a 12 month visa.

You can also get a 60 day extension of stay from immigration but only one time for each entry into the country.

After 90 days you go do border bounce in and out then get another 90 days

That visa is a year-long, multi-entry Non-Immigrant Type O visa. The way it works is you get stamped in for 90 days each entry. When the 90 days is running out you go to the border, stamp out of thailand, stamp in&out of another country and stamp right back into thailand to get another 90 day stamp. You do this for the entire validity of the visa itself (a year from the date it was issued)