I am just wondering if his blow-up was because of his guilt. If he is starting to do stuff with OW3 then he may be saying this stuff to you because he feels guilty and honestly wants out because he thinks he is bad, not because of you.
It is hard to say what to do. I know with me, there is one number H always calls about once a month (I have always wondered if it is someone he had a relationship with on the internet and it got further) so my brother called the number for me because i didn't have to courage to. I found out her first name, but that was it. You could look her up on FB or other places to see if you can find out who she is. Nowadays it is really hard to keep yourself private so there are ways to find out.
The ultimate question here is...what is best for you and what do you want to do? I think being direct is the best option, but that may not work with your H. I feel for you, really I do since I know of at least 4 or 5 OW some just internet things, others are full out infatuations with real people, but either way each one is hard and makes you feel worse and worse. Another thing to think about is H might have lied about the new employee's name.
I have no answers just support and hope you can find something that will work for you.
Me29 S3 H left 4/1/09 I file 8/2/10 Divorce final 5/17/11 1st http://www.tinyurl.com/25lhu52 2nd http://www.tinyurl.com/2c35ueg 3rd http://www.tinyurl.com/322yk89