What type of visa should I apply for if I frequently visit my Thai boyfriend in Bangkok?

Hi all, I need your advise. My bf has a job in Bangkok and therefore i am visiting multiple times a year, usually a few months on end. Until now I have been using the visa exemption on entry (30 days + possible to extend another 30).

But this time the immigration officer gave a warning, I will be refused next time if I don't have a visa. My return flight to Belgium is on 29 november, I need 2 more months in the Kingdom and want to try to get a 60 day tourist visa when I'm in Seoul next month. But not sure if they will grant it there...

Anyone with experience applying for a tourist visa in an other country?

Should I explain my situation when applying? My bf is born Thai (but Belgian nationality), he speaks Thai so maybe he can help.

For the long term I'm also not sure. Should I try to get an O visa to accompany him while he works here? We are not married, but together for 7 years. Also if we'd be married, unsure if they would recognize gay marriage in Thailand. Or should I get an ED visa and study Thai for a year? Or find a job and get a work visa?

Thank you