It is normal for American to just get one night stand or friend with benefit. if you are not like that, just tell him up front.
If he really care about you, he will change himself, but if he expect something more, he won't be with you long.
There are a lot of thai girls out there who are ready to spread their legs to welcome him. just think about it.
If you are lucky, he'll take you serious. But if he just wants to have fun, don't take it serious, just walk away.