1. Those jobs may still be open, reasonable people wouldn't hold taking another job against you. Work is work, and those who step back into discussion with you will show you a reasonableness that you will value more than before.
2. Situations like this is why sign-ing bonuses were invented. If you're COO of anything, you should also be able to negotiate a proper separation agreement, something like 6 months severance after 6 months of service. The signing bonus covers the initial bump, and then everyone has a window to see if things are copacetic. After that, it's a real relationship with consequences for dissolution.
3. You should be interviewing and considering companies as much as they're evaluating you. There's gotta be more to this story, some of which may be evident as you ponder what really happened. You've gotta develop that antennae. Asking to speak to a company's founders or advisors is a reasonable thing to do, certainly for a COO role that involves international relocation.
4. The "best guys" I've ever worked for f*cked me or our companies over. It's an important qualification to an extent, but character and vision and stability are secondary factors that will wag the dog, so to speak. Especially in startups. Startups are risky, and not always due to market forces or the brilliance of the business idea. Give yourself a good long notch in your work belt.