That sounds like an unusual situation after 27 years. That would be considered a valid marriage as long as he was faithful. could it be that he is so negative because he has done something wrong? Being negative and pessimistic is different than being verbally abusive, but being negative is a form of abusiveness since he is not honoring marriage vows and the Gospel which calls all Christians to be actively involved in being witnesses of salvation, and creating a spirit of heaviness in a relationship reflects an issue with divine relationship, or unresolved past issues. There is always hope. In the book, "The Bondage Breaker," Dr. Neil Anderson (or possibly one of his other books? "Victory Over the Darkness," and "Walking in Freedom," he describes a couple with a "hopeless" relationship both intent on a heated divorce, and he also thought that's what might be the outcome. But they surprised even him, who I personally refer to as, like Jesus, a "friend of sinners," It sounds like he is depressed, and could benefit from that ministry, or another local spiritual freedom ministry. Or definitely pastoral counseling. You can lead a horse to water, but you can't drown the horse. It is the other spouses responsibility after 27 years, to find out what the issue is, and put some consistent pressure on the reins leading the horse to the stream. Horses like water. I am pretty much terrified of horses, but, once many years ago, i rode one when I was younger. It was a hot day, and the horse decided it wanted to cool off in the small lake we were passing by. I tried to dissuade it, but the horse walked into the lake, with me on it, and rolled over in the water. The lady leading the riding horses assured me that the horse was one of her best horses and was surprised, and assured me that the horse was safe. I think I just walked back, I can't remember, but that began my fear of horses.
My family also had a horse that had an attitude, a mare, that really disliked men for some reason. And the horse knew all the tricks. She would grit her teeth for a half an hour to protest the reins and bit, then she would bloat her tummy to keep the saddle from being tightened. This way, when someone got on the horse, she could breathe out and loosen the saddle, and the person would just roll off, sometimes at high speeds.
Or she would bolt for the nearest low-lying tree branch to brush off her rider. So, I came to fear horses. Movies can sometimes confirm that horses sometimes just do what they want to do and can not be controlled, like the runaway horses. She was finally tamed by a lady and would not let anyone else ride.
And the Bible even says, "a horse is a vain hope for salvation; despite all its great strength it cannot save." (Psalm 33:17; NIV).
Many people put our hope in our cars, or things that are not reliable.
In this case, it sounds like your husband has become an unreliable horse.
Just keep leading him to water.
Keep increasing the positive leading, guided by the Holy Spirit.
Insist on pastoral help, marriage counseling, etc... It is his duty as a man of God after 27 years.
He is not only letting down his relationship with you, he is in danger of serious reprimanding in His relationship with the LORd.
If he doesn't deliver, it might require intervention, medical help, or other church/friends help.
sometimes a close male friend, a brother in the Lord, can confront him with his issues, and maybe risk being yelled at.
Men don't like to be told they are screwing things up. But, this is what God does.
"The Lord disciplines those whom He loves."
If he still doesn't deliver, just tell him you are going out. Or going on a vacation.
Take a vacation from your marriage.
Without him.
This helps with entitlement. He might think he is entitled to your company and is pretty much dishonoring your presence with his spirit of heaviness.
Anyway, be careful that he is not self-destructive, and it is safe to leave him alone.
Maybe this will help.
And this from a guy who was married for one year.
But, I have been in love before, and have seen what the hurricane of divorce does.
The bible even compares divorce to a "garment of violence," if it is a nasty, bitter divorce.
It's not that divorce is not allowed. It's just that we are called to the highest standards.
If it keeps up, he may drag you into a depression that might threaten your well-being and safety.
Then it would be grounds for a separation at least.
--from an expert single brother who knows very little about marriage.
But, Jesus was unmarried, except to the church, and understood relationships perfectly.
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I am glad for the ones stepping up saying "I hurt" "I need guidance" "I need help" Satan would love to see us all throw in the towel and miss out on Gods blessings! PRAISE GOD! Every time we stand up and fight for our marriages, it's like giving the devil a punch! It's like saying "You're NOT getting this one!" 
