Embrace it, and show your ex how cool you are. She will not be able to get you out of her mind. Talk freely with anyone who even looks curious. Tell them you feel proud to have lost out to such a fine Black man. Honestly, if you cannot date her, be her best friend. Tell him you do not want to ever come between them, as he did with you and her. But also say, you want to be her best friend and that you would love to spend time with them both doing whatever, wherever etc. He will admire you Im sure.I really want to stay friends with her but it presents it's challenges! Especially at social events with the three of us and either her friends (mostly white women) or his friends (mostly black men) are there. Lots of awkward looks!
And then........ down the line, when you and she are so close and so so past the awkwardness and any old ill feelings........ Propose to her