Is it possible to return to Thailand for a third time after two previous visits this year?

If by airline yes you can.

Possible for sure.

Sure.

yes can with plain

Can you get a tourist visa outside of Thailand? Like Bali or Vietnam?

If you've returned to your home country, the country your passport is from, and stayed there for more than a few weeks, you'll have to problems. Apply for a tourist visa this time before you come back. I've got friends that work two months on then one month off, and they spend their one month off in Thailand, entering on visa exempt everytime with no problems.

Anything is possible in LOS 🕶

Yes

You've been in Thailand for 4 months out of 6 months already. I think if you try to return to Thailand without a long term visa they are going to ask you a lot of questions.

If you want to live in Thailand you need to get a long term visa.

If you try to enter Thailand without a long term visa, at least have the 3 proofs that they will likely ask you for at the airport

1) Proof of funds. 20,000 baht or equivalent in another major currency IN CASH ONLY

2) Proof of lodging. At least 1 week hotel reservation.

3) Proof of onward travel. A plane ticket out of Thailand within the number of days you will get stamped in for.