If I was you I would get some tests made to check your infection parameters. Especially check for staff infections of various types. This could explain your symptoms.
If your girlfriend is in Thailand have her go to her local amphur (the one in her house book) and make an appointment for your marriage. Sometimes there can be a long waiting line so better to have an appointment setup. Same for the party venue if you want to have a party somewhere..
Honestly since it seems that you are considering to live in Thailand for life I honestly has to say it's a bad idea. The reality is that Thailand is not a good option when your an expat and very old. There is a reason that 90% of all old people at some point return to their home countries, and it's simply because the health insurance is extremely expensive when you are 75 years old if you will even be allowed to get get it. I would seriously consider another country for permanent retirement. EU comes to mind.. Maybe Greece, Portugal, Croatia, Bulgaria, Spain or Turkey?.. I have lived in Thailand for close to 20 years and moved to EU as it's much better suited for retirement. And unlike what you might think it's approx the same overall cost of living when you include the visa, insurances and so on..
The answer you are looking for, is no. Other than the stamps in the passport stamps no one will check. However it is possible to check but unless your a terrorist that will not happen.
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