I don't see what the big deal is about posting it on Facebook. Instead as a way to get attention, the OP could very well have posted it so that they won't need to call and notify every single person that'd want to know. Facebook, while a good site to get attentiom on, is primarily an excellent way of letting people know important things in your life. It is much easier to post something on Facebook than call every person you know and tell them.

Oh boy

What bothers me most is OP's name. Didn't do anything? Didn't call anyone to see if it was true? Didn't marry him? Didn't confront him or the girl? All the loose ends left with that name...

I Have had friends announce their engagements on FB. Everyone says congrats on FB and you call them. If the only person that commented was the girl who said he was cheating on you with her that either she's joking and you have shitty friends or she is telling the truth and your friends knew and they didn't know what to say.

At least that girl had the balls to tell you.

1) Confirm this is true 2) if it is, dump that bastard 3) if it isn't block that bitch

So people would congratulate you? That sounds just a tad shallow.