I am not married and my partner is Italian on a Non-b visa. As we are only staying 3 more months in Thailand, we decided not to go through the hassle of getting married and doing a dependent visa option as its very complicated and expensive.
My worry was around a VOA and a Visa exemption. Good to know that that won't be an issue, but I still can't find information on whether a exemption visa can be extended or not.