A. In short - No! Whenever we eavesdrop on phone conversations we only hear one side of the conversation. If he knew you were around he was hardly going to sound loved up with her was he? For all you knew, after you left the room, he could have apologised for being rude to her, and blamed the pressures of work. He is playing you and playing her. If you could control your emotions and not love him then it could work for you too, but unfortunately you've crossed the line and fallen for him, and we are all capable of doing that.
I date married men, everyone knows that, and I manage to control my emotions, but you need to see the bottom line here, and it may well hurt to read it. He is a father of two and one on the way. If his marriage is so bad, and he hates her so much, and he wishes he wasn't there, then why is there one on the way? You do know where babies come from don't you?
I'm sorry if it sounds blunt but you're better off elsewhere, married men have affairs, married men sometimes leave, but its rare. He won't leave as long as there's a reason to stay there, and another baby may well be the reason he needs. He's enjoying the adoration he gets from you, but he has still managed to get his wife pregnant, so maybe its not as bad as he makes out. Sooner or later the penny will drop, enjoy the fun while it lasts, but I suggest you start to distance your feelings if that's possible. I know how difficult it is when you're in love, but for your own sake, its best to face the reality of an affair.
When its good, its very very good, but when its dishonest its horrid :(