Freaking out about Mastectomy

Deep breath! You have every chance of feeling surprisingly well after surgery. Lymphoedema is not a dead cert even if lymph nodes are involved, stats are in favour of not getting it. I have lymphoedema and I garden, exercise etc. You are not going mad, just reacting to a very stressful and upsetting situation. Sadly, as we all find out, running through every possible scenario 20 times a day does nothing but use up your energy, which you need for other things. Write down questions so you remember to ask the right people. Talk to your medical team - you are both in this together and trust is important. Don't be afraid to ask for help. Everyone starts off knowing next to nothing and being scared to ask. Vent and rant here, it helps!!
Give that lovely fiancée some time, a good supportive man in these circumstances is a bit of a treasure! Breathe again, one step at a time and it will all get a lot clearer. Best wishes.