When you make Istikharah du'a, you're asking Allah to guide you towards the right choice, a special consultation with Him. But if the results don't turn out good for you, why was it facilitated? What was the point of your Istikharah?

Ibn al-Qayyim said, “If the veils were lifted and you could see behind the scenes what Allah does out of kindness for you, your heart would melt out of love for Him…”

Allah answers every prayer according to His time and plan and gives the best results for it. So when you ask for good, and something bad happens, know that it was His Wisdom that deemed what you thought was bad to be better for you. And when you finally decide to let go of the outcome you so desperately want and humbly submit to Allah's Wisdom, the tranquility you'll feel will be unparalleled.