Hi Nalo. This is difficult because I am not qualified to give proffesional advise and my advise might be biased as well. I will try and be neutral. This is all based on my personal experiences as well as the extensive reading I have done on the Internet.
Morbid jealousy is one of the delusional disorders. The are a few delusional disorders and you might find that your wife has a few of the others overlapping into the jealousy one. My wife had delusions of grandeur and persecutory delusions as well. Delusional disorders are linked to Schizophenia and Bi-polar though it is not a given. My wife had very slight Bi-polar tendencies. Go wiki Morbid Jealousy. When I first saw the definition, I was gobsmacked. I showed my wife the definition and she agreed that sometimes she did behave it that way. She only admitted it once and never again.
Consider the stance of someone with a delusion. It is similar to an alcoholic and a staunch theist. Until they admit they have a problem, there is absolutely nothing you can do to change their minds. I am not sure if medication will help because we never got to that stage. You have to first admit that you have a problem and that you need help before you get to the stage of taking medication. Delusional people are deluded into thinking that there is nothing wrong with them and that the rest of the world has the problem. Try climbing that mountain.
I am sure you are trying to keep your marriage intact. I tried very hard for a long time and was prepared to carry on because I had my own fears about getting divorced. In the end I had no choice because my wife said she has had enough of my screwing around and wanted a divorce. At the time this was earth shattering for me. After 30 years of marriage with 4 children I felt that I was being rejected and discarded for something I didn't do. I am not sure of your exact circumstances and can only guess that you are going through similar events. I'm waffling on a bit.
Based on hindsight, a year after my divorce, my advise is to get divorced and get yourself a new lease on life. This might sound harsh and as I said, I don't know your exact circumstances. If you feel you can cope with the divorce, I know that I thought I wouldn't but eventually did, then you will release yourself from the stress of being constantly accused of infidelity. It is soul destroying and depressing to be subjected to that kind of treatment. At the time, I felt that the way I got treated was criminal and I wanted justice. I wanted to sue my wife for all kinds of things because I felt so done in. I am over that but that is what it does to your mind. It isn't fair.
To try and justify why I would suggest a divorce is as follows: the release from the stress of unfair accusations, the way you don't have to tip-toe around in life waiting for the next flair up and the chance to get on with a more normal life is something you WILL feel immediately. Yes, there will be the heartache of the divorce and all the emotions that go with it but the long term benefits out way it all.
So,munless your wife willingly accepts her diagnosis and get genuine help, your are going to have to make a stand. It actually sets both of you free. Your wife won't have this cheating person to live with and you won't have to live with someone who constantly accuses you of screwing around. Win win. I know it is a tough one but be strong.
I really hope I have helped in some way. I am always afraid of giving the wrong advise. Keep in touch.
As a consolation, this is more common than you might think. I have met quiet a few guys that this has happened to. Just to let you know you are not alone. See if there is a support group near you and make use of your friends and family when they offer you help or support and most importantly, if you feel desperate, talk to someone before going off on a self pity mission.
god must love stupid people - he made so many of them