are you sure you love him very much?
If you did love him, you wouldn’t have lived in Korea for that long without seeing him for years.
In my opinion, it’s the booty call for both of you.. and there’s wrong with that.
Why don’t you ask him to marry you before you make any decision? Depending on what the answer is, you will know what to do. If he’s hesitant, then he’s just looking for a sex partner. if he’s willing to marry you and get the green card process going, at least he’s serious about a serious relationship.