Welcome to Just Answer!
I am sure you must have done almost everything to make your husband happy and comfortable, but it seems that as of now he suffering from Major Depression, and regarding his middle age this type of depression is known as Involutional Melancholia, which eventually has taken a toll in the form of a nervous breakdown and has lead him to take Such drastic steps as giving up his job , which as you have mentioned is quite unlike him.
But before, you do anything , you first need to be beside him at this moment , as he is suffering from major depression, and in any case should not be left alone.
As far as he being placed on lexapro which was of little help i suppose, as had the drug been effective , his present depression would not have happened in the first place.
So, i suggest that, instead of lexapro, he should be started on Effexor XR ( Venlafaxine extended release tab, which has prolonged duration of action) and along with this antidepressant, a mood stabilizer needs to be added, as a mood stabilizer keeps the abrupt mood swings into check and also controls the intemporate outbursts of anger that your husband has. potent mod stabilizers are --lithium, valproate , divalproax.
Besides this, for his anger control, he needs to be placed on psychotherapy (counselling), which will include cognitive therapy, response prevention therapy and anger management, and this will surely help him to control his anger. Psychotherapy is offered by Psychiatrists or clinical psychologist.
So, i would suggest you to consult a psychiatrist and discuss the medications and the psychotherapy that i have mentioned above, but before you do that , you need to get back to your husband first ,as he needs to be watched over by someone as of now, and then you may choose an appropriate time to convince him and coax him in seeking help from a professional. Once he is started on medications, and his symptoms start remitting , he will return to his job and start enjoying life again.
I know, it is going to be a tough job ahead of you in making your husband see a psychiatrist, but i do not see anyone else doing it other than you.
I wish your husband gets back to you and both of you start enjoying life as you used to earlier.
I hope my answer serves your query according to your satisfaction.