Moving on from a relationship based on lies

I dated a guy (34) for almost three years. Prior to that, we’ve known each other for more than a year through work. I thought our relationship was going so well. No big fights, he always talks about our future, marriage and all that. He was even insistent on announcing to the world that we are together (I’m more of the lowkey type).

Until I discovered that he’s dating another girl, and they’ve been together, longer than us. He chose her eventually. And me, I chose to let go.

It was all messed up. He could’ve ended it with me with just an apology for what he did. Instead he chose to break me more by saying that ours was all a mistake and that he never really loved me. He will never choose me over the other girl.

While I accepted that I was cheated on for years and that I need to do know is to move on, I still can’t help but think - how can people be so cruel?

TD;LR moving on from a relationship based on lies