I think that you can apply for an official separation order regardless of whether you live in the same property and can also divorce. I have heard of people that divorce whilst under the same roof and continue living together for years. Why do you think she might fight it? Does she want you back? Are you on good enough terms to continue living under the same roof?
She hasn't said is as many wirds that she wants me back, and that isn't an option anyway with what has gone on in the past. Yeah, strangely we get on better now than e ever used to do. Like the pressure is off, but I still want the divorce, and she has in the past said that she would agree to it. Eventually, Life will move on, and when it is economical (loans paid off, kids grown up and moved on, etc)we sill sell the house and go our seperate ways. Yeah, Ideal world I know.
I'm finding too that as soon as I decided it was well and truly over I have been less anxious and tense and much calmer. The anger I have felt has been as shock to me as I have always been a calm and placid person. I realise now it was because I was so hurt in the relationship.
It may well be that you can live under the same roof and be separated and even divorced. She can only refuse a divorce for 5 years anyway although at the moment that may seem like a lifetime.
The only problem I can foresee is if you meet someone else. I think feelings take a long time to disappear and if you suddenly started staying out at night she could start to be jealous, or, of course it could be her who meets somebody else.
I would consult a solicitor, once you have proper advise I am sure that you will feel better.It's the first step in a long journey.
Will be interested to know how you get on.