What an amazing situation on so many levels. I encourage the OP to do a full case study (
https://forum.mrmoneymustache.com/case-studies/how-to-write-a-'case-study'-topic/ ) to get better guidance. I also recommend reviewing the investment order sticky (
https://forum.mrmoneymustache.com/investor-alley/investment-order/) and the Bogleheads Investment Startup Kit (
https://www.bogleheads.org/wiki/Bogleheads%C2%AE_investing_start-up_kit). The Bogleheads wiki is a really fantastic source of self-education material that will cover everything pretty comprehensively. It is a lot to digest, so come back and ask questions.
You need to get your cash invested in a simple, LOW COST PASSIVE INDEX FUND portfolio in order for it to last as long as you do (or even longer). When thinking about what asset allocation you should have (usually a combo of stocks and bonds) you need to consider your risk tolerance (i.e. are you going to panic and do something silly like cash out when the market drops?) and your longevity. More bonds will mean less volatility, which makes some people more comfortable. More bonds also means lower average returns and that your money will run out sooner. The general rule of thumb is that you can live off of 4% of your invested assets; a great thread on the robustness of that rule-of-thumb is here (
https://forum.mrmoneymustache.com/investor-alley/stop-worrying-about-the-4-rule/). It is absolutely possible for you to set your situation up like an endowment where your money will live there forever; you need to invest it properly and have a really firm handle on your spending to do this. Obviously you need to get back to the states and figure your new life out to know what your spending will be, but make those choices consciously, as others have talked about.
Finally, I'd recommend studying the Bogleheads wiki entry for how to manage a windfall. I realize that isn't exactly your situation because you've earned and saved this money, but the mechanics are going to be similar. You haven't thought about the money because you haven't had the time, and it isn't invested, so you need to make the same kinds of decisions as if someone just inherited $6.5M.
https://www.bogleheads.org/wiki/Managing_a_windfall The key points on this are to: take your time/don't make any hasty decisions, educate yourself, and create a plan.
If you need some hand-holding, then I recommend either the Vanguard investment advisors
https://investor.vanguard.com/financial-advisor/financial-advice who will be the very cheapest you can pay for that level of service, or a fiduciary CFP
https://www.napfa.org/who is someone who is required to act in your best interest. Be very, very wary of any slick salesperson, anyone who wants to pay for your free meal to talk about advising services, anyone who wants to charge an "assets under management (AUM) fee, anyone who can't very clearly explain how she/he is paid, or wants to charge anything over a TOTAL of 0.3% for investment advising services. If I may be perfectly frank without offending, you would be a wonderful mark for an unscrupulous advisor because you have significant assets and very little personal knowledge of how to manage your money. Ask lots of questions, don't make any sudden decisions, and make sure you understand what you are doing and why. Come back to this community to ask questions and learn; there are a lot of smart people here and on the Bogleheads forums who would be happy to help.