Passed over for promotion unfairly..

100% qualified for a position, already doing the job. Have been passed over a couple times for it, each time they give me a chance to interview and then end up for real, picking a relative (so and sos niece) fresh out of school for the job - Nepotism is SO rampant in this organization.. anyway, President (big big boss) of company pulled me in this time to say that his nephew is going to take the position but wanted to let me know that he promises I will be next in line.. that he’s sorry I may not get it this time but he’s got really big plans for me.. including listing me as a a filling a spot for the 3rd higher up in the company eventually ...so devastated.. and just frustrated.. should I show grace one more time? Because it’s a huge company and pay is amazing. Or should I start looking ..is there a side of this I’m not seeing like “cheer up, be patient, it’ll happen for you” or is it more like “screw those people you’re stupid if you believe them after all the carrot dangling they’ve committed” ... I’m a total rockstar, highest performer and a great manager at the same time so they’d be really missing out to lose me.. financially.. I close multi million dollar deals..thing that keeps me hanging is they PROMISE I’m next and they’ve acknowledged they messed up and my chance will come. Help