I'm completely with Beverley on this. You still view your husband as a good person. From the outside, in my opinion, to treat his wife in the way he's treated you makes him absolutely not a good person at all and an even worse husband.
Mid life crises don't excuse what he did. He messed you around and kept you in the dark for months, talked you into having an termination whilst knowing he had another woman pregnant (do you think this might have been a major factor in why he insisted on you having a termination? That he couldn't afford for you to have a child, in which case, why didn't he use protection with both of you?). Have you been tested for STI's? He's jeopardised not only your marriage but your health too.
If he had been open and honest, discussed what was going on with him and actually left you, then you reconciled after all this, I would advise working on things and getting counselling if you really want it to work. As it is, with the way he drifted in and out of your life selfishly getting two women pregnant when he couldn't afford to have more children, basically serving his own needs whilst making you feel suicidal, I can only say LTB.
Don't go round to the OW's house. That's the worst thing you could do. She has every right to call the police if you turn up and start shouting and acting aggressively towards her.
You don't know what lies your husband span to her or what their relationship was. The fact that she wants nothing to do with him is very telling, along with your husband not wanting you to go alone. I abhor cheats, I wouldn't do it nor stay in a relationship with a cheating man, but I don't blame the woman for not answering the phone or wanting anything to do with him or you.
The baby might be his, it might not be. You can't force her to confirm this or communicate with you, and you can't force her to stay away. Your husband brought this to your door, not her. She isn't blameless but the impact on your relationship is solely the fault of your husband.