Don’t give up so easily. Its not easy to secure an overseas
position.
If you are homesick, you are probably not busy enough and that
causes boredom.
I have been in China for the past 5 years. Its a rollercoaster
ride.
Some of the things you can do are:
1) Travel all over Japan in weekend trips. Not to tourist places,
but to interesting places you can find.
2) Develop some hobbie, Some Japanese are cool with weird ideas and
you can learn something in the mean time to bring back singapore
eventually.
3) Work parttime. Not for money, for expanding your circle,
changing your environment.
4) Do some business. There are people that wants to buy Japanese
stuff. (i am one)
5) Change your personal life. Get a partner, get married. Have a
kid. Your time will be gone in a flash.
Lastly, remember why you wanted to go there in the first place.
Hold on to that emotion.
Great and helpful advice. You definitely sound like
one who works overseas.