So, when dating someone from Thailand there will most likely be many trips that you will make to her or his home country and there are many options for travel.
We live in New Zealand so we have found there might not be as many options as one would like for cheap travel to Thailand compared to say Australia for example.
The options we have are Air New Zealand, Qantas, Jetstar, Malaysia Airlines (good idea to update your will for this one), Emirates, Thai Airways, and the new service from Air Asia ex Auckland.
The prices can vary depending on when you are looking to travel, and we normally book to go back to my wife's place on or around Songkran festival so we try to keep a good look out for cheap flights.
I find it pretty good to regularly check each airlines website and investigate dates for travel and as long as you can be a little flexible then you should get a good deal.
For example, I have seen flights from NZ to Bangkok return for $600 NZD which is really good but I like to have a little service on my flights and seem to book through other airlines.
For our next trip (when we have our traditional thai wedding), we originally looked at Thai Airways but the flights were about $3500 return direct for the both of us. This was getting up there, we we opted for www.cheapflights.co.nz which ending up saving us well over $1000 !!!
We do however have to transit Hong Kong on the way up there for 9 hours but neither of us have been to Hong Kong so it will be a good experience shooting into town for the day before flying onward to Bangkok. The flights ended up being booked through Thai Airways anyway and we get a direct flight home so I'm happy with the savings ;)
So, it does pay to shop around when looking for flights and just keep an eye out on the deals.