Wife's depression! Husband needs some help!!

I don't want this to be too lengthy. My wife has been diagnosed w/ Major Depression by a Psychiatrist. They also believe her Thyroid has a lot to do with it as she has Hashimoto disease. She is having both hypo/hyper @ the same time. Her thyroid levels were above the labs values. Off the chart. They are still extremely high.
During this time my wife said she thought our marriage was over and she wanted a divorce. She called me every name in the book and said things that still to this day have deeply scarred me. I found out she was seeing a man that has been chasing her for 15+ years. They did kiss and that was it.
She had been on Celexa but when the MD diagnosed her they put her on Remeron. It took awhile but things got better about 5-7 weeks. I am pretty sure she stopped taking them and then told her MD that she is doing better but is always tired(side effect) and the MD told her to stop. Then about 2-3 weeks after that I started seeing the depression again. Mood swings, and etc. It got real bad again for a 2-3 day span.

She gets very defensive when I ask her how she is feeling or how her appointment went. All I want to do is help or find a way to help.

THis is where it gets frustrating and hurtful. I try so hard to help her and let her know I love her yet most of the time I get little emotion back from her. I do wonder does she really want to be with me and etc. She says she loves me and wants to be with and I make her happy but it makes you think. A lot of the articles I read about Spouse's depression is that it is actually harder on the spouse that does not have depression.
I need my sanity as well but even when I try to do something to get my mind off of it I can not. Right now it is 24/7 thoughts/concerns over my wife's depression. She is finally seeing a counselor as well today but that took forever. She thought she could do it by herself. She if very stubborn.

I plan on seeing a counselor as well as I need someone to talk to on how to handle this situation. Does anyone have any help or in a similar situation. It is very tough and I have 3 kids as well. I want to stay with my wife forever but what if she does not get better. My kids and I need a healthy household. Any help would be greatly appreciated. THANKS!!