How do you trust again?

When you’ve been cheated on by the love of your life, the person you thought you were going to marry. After your trust has been completely shattered, how do you learn to trust ANYONE again? How do you get back into the dating pool after that? I feel like I’ll never be able to trust anyone at all after this. He was the last person in the universe that I thought would’ve done this. So...how? How did you do it?