I am interested in marrying a man who is pious and we are loyal and serious about each other. But he did an Istikhara from a scholar and it came out negative. We are so worried and are wondering if there is any way for us to get married?
The first question is why did he do an Istikharah if he is absolutely convinced on wanting to marry you?
Either he is two-minded and indecisive about it, or he's confused, or he doesn't know what istikharah is.
He must first make his firm decision on what he wishes to do, and whether he wants to marry you or not.
As for the istikharah turning out negative, what he can do is pay sadaqah, wait a while, see if circumstances have changed, see if he is decisive about his plans, and then either go ahead with marrying you or not. If he's still reluctant, then neither he nor you should waste any more of your time. Wish each other the best, and pursue your lives without being worried, as for sure more marriage opportunities will come your way.
With prayers for your success.