maybe hes been dating that person longer and he was dating you at the same time

You broke up yesterday but your relationship was over a long time ago.

I'm sorry to hear that. But it's obvious he already dated her while you two still dated. So you know you have made the right decision to let him go. You deserve better.

This is someone who clearly moves on without a second thought, and has most likely planned it all before your breakup. I'm sorry, OP. Let's hope you don't get some time waster next time! x

He must have gone to vegas

Well it's not funny, but that made me laugh. How did he make the announcement? Who initiated the breakup? Is he maybe possibly faking it to mess with you?

Good thing that guy's not in your life anymore

I had the same thing happen once. I broke up with a boyfriend I had and he got engaged within a month, and then they broke that off a few months later. But one day is quite a record.

I feel sorry for whoever he is engaged to.

In my experience, if someone is willing to cheat with you; they are willing to cheat on you. Assuming that he's been cheating on you, he's probably setting himself up for a lifetime of misery. Hopefully that makes you feel a little better.