PhD Candidate to resign and reapply; Asking recommendation from thesis advisor
[1]. No funding.
[2]. Work for 7 - 10+ years in PhD.

Combining [1] &amp; [2] gives an unrealistic expectation from the supervisor for you to stay. 

I had to assume you are doing your PhD part-time. Getting a reference letter does not immediately require resigning or quitting. Even if you apply now, you will mostly wait till the next academic year before you quit. That is almost another year. 

Your work so far may not even be wasted. When you join the US school, you may still collaborate with your local school, and even have more joint publications. With funding, your focus will be higher anyway, as a full time student.

There is nothing that should prevent a fair supervisor from writing such a recommendation letter. You may even convince him that you are not quitting - but, rather halting. Given that you are in your 7th year, it might be just months away for your graduation.

Hope your supervisor will understand and provide you with the letter. I have a friend who got a recommendation letter from his ex-PhD supervisor and successfully joined this another funded program in a foreign country. What you are encountering is not really a rare case.