I had to leave Thyailand last Saturday with no notice so i was unable to get a re-entry visa , i can go to the Thai consulate in Cardiff and obtain an O visa with my Marriage certificate , should i get a single entry or multiple entry o visa , if i get a singl entry does that mean i have to leave Thailand in 90 days and get an extension or new visa ?

I had to leave Thyailand last Saturday with no notice so i was unable to get a re-entry visa , i can go to the Thai consulate in Cardiff and obtain an O visa with my Marriage certificate , should i get a single entry or multiple entry o visa.

Multiple or single is really up to you.

Single if you have the money for a 12 month extension

otherwise multi-entry may be what you need.

if i get a singl entry does that mean i have to leave Thailand in 90 days and get an extension or new visa ?

A single entry will give you 90 days, which can be extended in Thailand based on Marriage,

if you have the necessary finances.

Otherwise you will need to leave and get a new visa

Yes. Single entry 90 days. Then you will have to leave or extend for 12 months if you can meet the financial requirements.

Multi Entry . As many entries as you want with a limit of 90 days on each entry. This would give you up to 15 months.

if i get a 1 year multiple does that mean i stay in thailand 1 year without the need to leave the country every 90 days

if i get a 1 year multiple does that mean i stay in thailand 1 year without the need to leave the country every 90 days

No, it means the visa is valid for one year, you get stamped "permitted to stay" 90 days each entry.