I would make sure you don't say anything hurtful to him outright, just act happy like you said you were.
I really would reccomend not moving towards him right now, its a tough call I know, but it really sounds like the space you are putting between you two is having an impact. Throwing that space away to run to him likley isn't going to have the impact you want is my guess.
Also, if he's misreable around OW, then she won't want him around her either...the last thing you want to do is cheer him up so she will want him more.
I would leave him wrestle with his demons for a while. He doesn't sound like he's going anywhere in the next nine days.
