There's no limit, but letting you in is at the discretion of the IO. If he/she suspects you're 'living' in Thailand you can be denied entry and told to get an appropriate visa. Chances are, you won't have a problem next time. If you're concerned you can get a Tourist visa.
says has a good reason to return to Thailand. She will need to demonstrate she has the finances to cover the trip (or you do if you're her sponsor). Good luck!