Flash Sentry was the only one Twilight had ever had a crush on. I've seen the answer too. But It's not true, It's someone's idea. It Is hinted at that Rainbow and Applejack are together In the final episode. Twilight Is shown to be single, Just like Rarity and Fluttershy. Pinkie Pie ends up with Cheese Sandwich and they have a son In the future.

I don’t think Twilight is straight
With a little research I found she is married to Rainbow with a child