M.,
First, I am so sorry you are faced with a potential divorce. You didn't mention how long you have been married or how long you and your husband have been in ministry. Do you know why your husband feels that things are hopeless? You also didn't mention whether you desire to stay in the marriage and see it healed.
My guess is that you have already been in marital counseling. That is always a good place to start even though it is hard for both parties initially. If you haven't tried counseling,that is the place to start. Just be prayerful about where you go. Perhaps this site will allow others who have benifited from marriage counseling to recommend a good counselor.
The obvious place to start is where you are-- at church. It would be helpful to call a private meeting with your church elders and let them know what is happening. Unless your church is completely independant of any affiliation, you should also contact your bishop or the person or board that your husband is accountable to. Keep in mind, that pastors and their wives are subject to marital problems just like everyone else; perhaps more vulnerable because your time and attention is often given out to others, leaving little energy for your own relationship. It is not uncommon for pastors and their wives, worship leaders and their wives, and other leaders in the church to experience serious marital problems. However,divorce is not the answer in most cases.
Your board of elders or bishop will be able to counsel your family, and counsel your husband in particular. What is customary in situations such as yours (in Bible-based churches) is that church leadership immediately takes action to remove some of the pressures and responsibilities from their pastor and provides some time for him to focus on his wife and children. Having a weekend off per month for a season allows you and your husband to separate yourselves from the ministry and focus on your family and your own personal relationship with God. They would normally provide counseling outside the church as well. Steps beyond that might include the church borad asking your husband step-down from his role as pastor for a season (while continuing his salary) while you and your husband work toward reconciliation.
Is your husband reconsidering his call to ministry as well as his committment to his marriage? Does he have an actual plan to start divorce proceedings or is he speaking out of pain and discouragement when he says that he doesn't believe things will ever change between the two of you? Has he thought through the consequences or ramifications of his filing for divorce? Does he think he can continue on pastoring or does he want a secular job and a totally different life? If this is the case, his desire for a divorce may be resting on much more than his relationship with you.
You are correct in your concern that a divorce has the potential to harm church members. The church is another kind of family and anytime a family is fractured or broken, everyone in that family suffers. The role of a pastor is much like that of a father. This is another reason to involve the church elders and start raising up prayer and emotional support within the church. (scriptures that come to mind are: "submit yourselves therefore, one to another,"," If anyone is sick, let him call for the elders of the church. . .", "When one part of the body hurts, the whole body suffers . . ", "Bear one another's burdens . . ")
If I could speak to your husband, I would remind him that the God he has chosen to serve is a God of healing and reconciliation. No relationship is beyond His reach. From scripture, we already know that God hates divorce and thus when you pray for healing of the marriage relationship, you do no have to doubt that you are praying according to God's perfect will.
You and your huusband need to speak with a third party who can pray with you and help find a foundation of agreement for you and your husband to rest your marriage on while the difficult parts of the relationship are dealt with using the wisdom and kindness that you both need to heal. Remember that as Christians, the Lord himself is our sure foundation. It is a foundation that cannot be shaken if both of you trust in Him and are committed to your marriage and your vows.
Pray as a family every day. "The couples who pray together, stay together" is not just a cliche'. Very recent statistics show that every area of married life improves when couples pray together: communication, forgiveness, and intimacy . . . while negative attributes of the relationship diminish: hostlilty, arguments and resentment.
Read the psalms daily and the promises of God found throughout the Bible. This will encourage you. Also pray and ask the Lord to give you wisdom in your words and actions to your husband during this season of conflict and confrontation.
My prayers are with you. God is faithful.