Emily your marrying will not get you Thai Citizenship not never wont happen. It will allow you to apply for a visa to remain in Thailand based on Marriage. If your baby has a Thai Birth certificate with your Thai Bf's name on it you can apply for a visa as you are looking after a Thai citizen. He is your dependant. As to the babies English Citizenship the UK allow dual citizenship Thailand doesnt but they dont check. It is a Non O visa just the same as if you are married except rather than to visit spouse it is to visit children as in yours.

Getting Married does not mean you get Thai Citizenship. However if the Father is Thai and is on the Birth Certificate then the baby is Thai. I believe the visa you are looking for is a depandance visa. This has more or less the same requirements as a marriage visa.

Only if the overstay was more than 90 days you would then incur a one year ban. However if you had been caught at any time on your overstay you would of been imprisoned escorted to the airport and deported and have to pay for the privilege. You would also of been banned from the kingdom for 5 years. .

You are giving away a lot of money to save on a little paperwork if you wanted to do that just use a lawyer or a visa agent much cheaper. However given the OP's plans in Thailand which is to work it would be a total waste of money.

@Franck *****************

With many visas you dont have to leave every 90 days i.e. Dependant visa, marriage visa or retirement visa. You have to do 90 day reporting and that is it. I believe that you can even do that over the internet though its not working fully. Given your prospective plans it would be a waste of your money and useless to you. You might look into the digital nomad visa or just one based on Business.

If you get married to a Thai. I cannot say for certain and I dont like to give incorrect information but I seriously doubt that her visa status as a Swedish national has any effect on yours. No doubt a visa agency could give you a definite answer but I have never seen anything that would make me think that it does. It seems a lot easier for you to just hold on till you are 50. Besides marrying your lady should be a choice based on other factors than your visa status.

Well under 3 years to go seems easier for you to hang it out

The thought occurs if the adoption paperwork is fake then i actually might be easier as you dont have the adoption to cloud the issue. I am not sure of this but it may well be that if you are adopted than you may of had to give up your Thai nationality. I really dont know.

As I said she would have to get that sorted first. Track down her original Birth certificate otherwise you are in the same boat as any other farang. I presume you are to young for a retirement visa a Education visa might be an option for you or get a job here.

Certainly you are married to a Thai. She would have to get her Thai nationality sorted first. Then you can get a Non O visa based on marriage. Look it up If I remember is 400k in a bank for 3 months. Subject to 90 day reporting lasts a year and costs 1900 Baht. As to getting her Nationality sorted as long as she has her documents then not a problem. Strange that she has not already done so as then she wouldn't need a visa. If I remember correctly you have to tell them you are given up your other nationality but they have no way of checking.