They are funny about having the appropriate visa. So if you want to volunteer without any trouble, you should get a volunteer visa. However, I have carried in my neighbors groceries for her a few times,( don't tell).
Did he come in visa exempt,( then have flagrant disregard for the law), and stayed an additional 150days @ 500bht per day(75,000), caps off at 20,000bht with a ban of X amount of years. That's what this sounds like?
A K1 visa, I'd recommend. I did it and it takes around a year but you chances are good you'll bring her back. Everyone told me it wouldn't happen and diligence will pay off.