I'm really sorry you're hurting. He's betrayed you SO many times (isn't this four now?) -- I cannot even imagine. So let me say that up front.
What do you do? I can start by telling you what you DON'T do, and that's you DON'T go looking for TRUTH from either your husband or his girlfriend. "All cheaters lie -- PERIOD." Repeat that over and over 500x until it sinks in. You will NOT get keys or answers from your husband -- he's fogged out. He's addicted. His brain is riddled with endorphines and chemicals that make otherwise sane adult female astronaut drive across country WEARING AN ADULT DIAPER to go defend her man's honor.
He's an addict.
You are looking for clues from him, and not only is NOTHING he says the truth right now, your very pursuit of him is hurting your case. STOP IT.
Secondly, DON'T TALK TO OW. She is NOT your friend, and your contact of her only elevates her in importance (think the President of the United States, agreeing to sit down and negotiate with some rogue Third World terrorist). If my admonition isn't strong enough to persuade you, let me tell you this in all certainty:
When you do that, they talk about your contact of her, and they laugh about you.
I'm sorry, but it's true.
For the time being, you have to move on -- legally, physically and emotionally. The GOOD news is, given his past track record, your husband is about 95% likely to come crawling back to you -- I predict in as little as 60 days or less. How you respond THEN will be our opportunity, but that won't come until later.
For now, we need to take care of Sandy, and of your family, and show you ways to get past this immediate pain. For starters, it helps to think of your husband as an addict -- that will help you with forgiveness, and will put things in the proper perspective.
Again, I'm sorry. We all saw this coming, and the reason I was so tough on you before is that we didn't want to see you go thru this incredible pain a fourth time.