Anonymous participant do understand that there is a queue that determines who's application is processed next. The earlier you submit your application, even during holidays, the higher up on the queue you are. Keep that in mind if you decide to wait.
to make it work you first get married, then you get your type O visa before you come to Thailand, get your Thai bank account, transfer in your bt800,000 to meet the requirement to get your one year extension. Once you have your one year extension on your type O visa based on retirement then you can apply outside Thailand for your spouse's visa based on dependent. This is now how getting a dependent visa extension works. If your spouse is 50 years old, or older, immigration can require both of you to have retirement visa extensions. If you don't get married then immigration treats you both as independent people. They don't recognize "fiancee".
Anonymous participant that has happened to others. You got a 90 day ED visa. At the end of those 90 days, with paperwork your school gives you, certifying you are going to classes, and making progress, to get a 90 day extension, taking you to the end of your course.