If you are a foreigner living in Thailand then you will always be considered richer than everyone else, except by close Thai friends who have built up an understanding of how rich you are by observing how you spend your money.
There is a very strong sense of who should pay between Thai people. Typically, the older person would always be expected to pay. Between friends a lot of kudos can be earnt by being the one who paid. Especially at dinner, after all food is cheap.
Thai people don't like to mention money in many situations and they don't make a big deal out of it on the surface. When they are with older people or people who are perceived to be of a higher status like their boss it's polite to let them pay for a meal. However, it depends on the situation as well.
Sometimes your boss might pay for you. Some bosses pay every time! Some people avoid going out because they know they will get the responsibility for paying. If you think it's your turn to pay, don't ask. Just pay. When the bill is split between everyone, it's called American share.
In Thailand, traditionally the man would pay for everything when going out with a woman as most men were perceived to be able to earn. In modern Thai society where women also work, women sometimes pay but men are still expected to pay most of the time.
A typical situation might call on you to say
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