Mike is right,
Dark things can happen.
Even a court ruling from another country saying you have a right to access to the child is ignored by Japanese Gov
(This MAY no longer be the case, I know many were putting pressure on japan for this, they didn't sign a treaty that also stops child sex trafficking - same treaty btw)
You could of course ex out of the country darkside, but that is somewhat expensive.
With costs varying on who and what you know, and by the sounds of it in your case it will be expensive.
Also immigration people tend to be real bar-stewards
it will cost and it will be a nightmare, and again. you are completely exposed
Yes you can put in some guarantees and fall backs for yourself, but again
who and what you know.
If he wants happy family life, then yea.
Put a ring on it, even if it's only a paper marriage.