Help to guide him that he is now reading the Bible. He does not have to run to her every time she is falling apart. In order for him to break this cycle, he has to put a stop to it.
In some way, you must let him know that satan is using this other woman to continue his war that is going on inside of him. Some how, that he is now reading the Bible, explain marriage to him and that adultery is killing him spiritually.
That if he leaves to be with the OW, that it will fall apart because of it being adultery. That in order for him to get past what he is going through, he is going to have to put an end to that relationship. Not the one with you.
Remember, adultery causes spiritual death. That is the reason for all that he is feeling inside. He is not responsible for what she is going through. Satan is responsible for what she is going through and that is what she needs from him and you is prayer for the binds of satan to be broken that are around her.
She does not need your husband, she needs the Lord. You need to make him understand this. The Lord is getting him into the word and your husband is searching. Now you are the one that needs to lead him with the Lord. He is not completely understanding everything that he is reading and satan is going to twist the word on him because he sees what is happening. As you should be seeing the same thing.
I think that it is awesome that he is reading your Bible. This is in answer to your prayer. Now you need to help him to understand what he is reading by praying that the Lord will open his eyes. Together with the Lord, you and your husband have the power to win this battle, but separate you don't.
If you have a Concordance in your Bible, look up marriage, and look up adultery. Read what the Lord has to say about both of them. Understand the Spiritual side of them and not just the natural side of them. Understand the Spiritual Consequences that your husband will suffer if he continues down this road.
It is not okay for him to keep running to her because of her insecurities. Satan is using her to keep your husband in turmoil and your husband needs so much prayer. Your husband is a good man in spite of his actions. The Lord created him and loves him as much as he loves you.
Your husband is screaming so loud for someone to love him enough to pull him out of this turmoil. As I know that you can not pull him out, but you can guide him. He is screaming for answers and is willing to take death of his soul just to get out of it.
He is screaming for someone to love him enough to help him. Do you understand what I am saying? This isn't the man that is screaming as loud as it is his soul. He wants to feel the love that only Jesus can give him. He wants a reason as to why he should leave this OW and stay with you or why he should leave you and stay with the OW.
This OW does not love your husband in the same manner that you do. Her love is out of desperation to take her pain from her and your love is pure and you love him because you chose to, not because you have to. That is what he needs to understand. That your marriage is not just about sex. That you want him in your life because you choose to have him in your life and you choose to love him. That you unconditionally love him and he needs to hear those words from you.
What he is hearing from this OW is that she needs him and will do whatever she has to in order to keep him. What is she going to do with him once she has him? Is she going to find him to be so desirable once he walks away from his family and she no longer has to fight for him? Is he going to be everything that she thinks he is? I highly doubt it. That relationship will not last because of the way that it happened between the two of them. It is destined for destruction and what will that do to your husband?
There is such an urgency in my spirit about this for your husband. Read the scriptures on marriage and adultery. Teach your husband about the unconditional love that Jesus has for him. Teach him about the salvation and help to end his turmoil by leading him to the only person that can help him and that is the Lord. You will never be able to give him what it is that he is looking for any more then that OW will be able to. The love that he is looking for, only the Lord has for him. All the demons that keep trying to control him will no longer be able to stay once he receives the Lord. Then you guys can build a solid marriage on the Lord.