Firstly, I'm so sorry that you're feeling like this. When you're at rock bottom, I know how hard it is to see a way out or to break the cycle that you go round - particularly with stress disorders and anxiety. But, there is a way out of the loop. And I have every confidence that you will be able to find it.
You've highlighted the negative thoughts you're having, and that is a strong indication to me that CBT (cognitive behaviour therapy), might be a program that you would considerably benefit from. It's something I'm going through at the moment, and I'm slowly starting to see the benefits and understand how my mind is working. It's difficult to put it into practice sometimes, but at least it feels like I'm on the right road to getting it sorted. I don't know if you've experienced the feeling also that you know something's wrong, but don't know how to go about getting yourself well again.
These type of mental health problems are always difficult for the sufferer's partner, and it hurts them because the person they love is hurting. Often they feel helpless as well, because ultimately, they just want to make you all better and take away the pain.. but they don't know how. The truth is, they can't. This is something that has to come from you, and you need to be able to being to recognise where your negative thoughts are coming from, why you're having them, and then think about whether or not they are justified - is there any evidence to support them? This is what CBT is all about - training your mind to be truthful rather than (unecessarily) punishing.
Your problem is quite common with perfectionists, and CBT has been shown to be a significant help in these cases.
For some quick tips on helping yourself to calm down when you can feel your heart rate rising, your body temperature rising, and your mind starting to spiral out of control:
1) Breathing techniques. It sounds so simple, but it really helps if you can get the hang of it. Concentrating on getting your breathing to be steady and smooth, and making full use of your lung capacity. Breath slowly to reduce your heart rate.
This works because often when we start to get stressed or panicked (mentally), our bodies react physically - adrenaline rush (causing sweaty palms, faster heart rate, and shakiness). Because this starts to happen, and we're not actually "in danger", our head says "oh my gosh, what's happening to me?" and we start to panic more. By getting the breathing and heart-rate back to normal, it helps to supress the rising panic.
2) Muscle relaxation. If you're in a place where you can, lie down and concentrate on every single area of your body one by one, starting from your feet. Clench your muscles for 10 seconds or so, and then release. Doing this will help your body to recognise when your muscles are tensed up, and gradually, it will "learn" how to untense them in normal situations.
The most important thing though is to be able to rationalise your thoughts. I can't recommend CBT highly enough, and I would really advise going to see you doctor to see if he can put you in touch with a counsellor to go through the technique with you. Alternatively, there are some good handbooks on it. I'll try and dig out the titles for you.
Keep talking to your fiance, and letting him know how you're getting on. If he can see that you're actively seeking help and trying to get better, he will feel better too, because it will no longer feel like his responsibility to make you better. The first thing my boyfriend said when I started talking about my counselling sessions was "I know it's hard for you, and you're doing really well by getting help. I'm not going anywhere, you just make sure that you're getting better, because you deserve so much more than to be feeling like this."
Just the words "I'm not going anywhere" suddenly lifted a weight off my shoulders.
Best of luck. Take care of yourself, and find your inner strength again. It's there, you just need to find it.
Take care, C xx