I will be applying for a 3 month non o visa and staying with my wife in her house and will be applying for a marriage visa .so i will not be able to put a return flight in the application what should i do

Non-O retirement. I used a date 90 days from arrival. I was later asked for travel booking information from the UK but not asked for any departure travel details. The application actually only asks for "intended" travel dates so ought not need to be totally accurate, despite the subsequent request I received. Non-O granted and subsequently extended, no issues.

23 minutes ago, gosmk10 said:

so i will not be able to put a return flight in the application what should i do

Not required. Just put a date within 90 days of arrival.

BTW: assume you have a Thai bank account in your name? Which bank.

You won't be applying for a marriage visa.

You will be applying for 12 month extension to your permission of stay.

1 hour ago, gosmk10 said:

I will be applying for a 3 month non o visa and staying with my wife in her house and will be applying for a marriage visa .so i will not be able to put a return flight in the application what should i do

I applied for a Non O 90 day visa based on having a Thai spouse earlier this year and in the return flight part ,all you need to enter is any date after you arrive and a flight number.

You don't need to have booked the flight ,just look for the flight number as if you were going to return.