Welcome back, sorry that you had to come back in these circumstances. You have done so well to make it 4 years free of self-harm, that is a fantastic achievement and something to be proud of.
It's understandable that things have fallen apart a bit, I think anyone in your situation would struggle to cope. Do you have any supports? I found some
information on carers for people with cancer that you might find helpful, they even have an online community that you could use to get some extra support from people who are going though the same thing. Also it sounds like your fiance is getting some good medical care so there is a good chance that he will get through this. Don't lose hope.
As for the self-harm urges, try and remind yourself why you don't want to self-harm. Maybe you could even write a list to help remind yourself. Also you can find some great distraction ideas
here. Remember that you are stronger than you think, you can get through this. Take care
Kat xxx