Ok. Let me get this straight. Your W is having an A with this man. Just comes himself. He has children YET he doesn't bring them to a child's party. Just decides its appropriate to show up at a party that is thrown by someone who could take him down.......
Wow. Without words.
But.......
You know whose fault this is. Your wife. I am sure she encouraged him to go, said he has a 'right' to go. She is unbelievable, so disrespectful of you and your girls. And to prance around the party with OM and her H in the same room. Those people at the party probably think she is a fool. Of the three of you, YOU were the bigger, better person. W is an adulterer, and OM is a sleaze. You were the father of your beautiful 3 yr old. W is pathetic.
Don't beat yourself up for the people feeling sorry for you. Think about it, if you knew someone in your situation, you would feel sorry for them. Its not pity, its different.
Awful, terrible situation. I know what you mean about your face feeling red and flushed. When I end up in a room with OW, its almost impossible to breathe or smile. I am not kidding you when I say my face muscles don't work. HUGS to you.