Get yourself down to a solicitor but it doesn't have to be Monday - do your research, get a good 'un who is firmly on your side. Perhaps ask around on MN for good solicitors in your area.
As mine says 'every case is different' so you can't be certain that you'll have to buy him out of the house. My husband walked out ten days ago. It sucks to be us right now. However, having seen a solicitor I learnt:
The length of time you've been in a committed relationship not just married can be factored in (she cited a Mostyn judge/case?)
Also, having given up your career will be a factor (I did four years ago).
Also, your earnings v. his earnings.
What he brought to the marriage v. what you did.
The costs of you rebuilding your life, v. the cost of him carrying on with his life.
It is assumed that both parties will be financially disadvantaged by divorcing, but it is not assumed that you have to have a massive imbalance in who it costs and how. The starting point is 50/50 but rarely are assets divided that way.
Also, guilt and the need for speed to end the marriage, means sometimes people give away more than legally necessity.
Sorry, love it really is a horrible time, I know. I panicked for a week until I could see a solicitor but it has helped me process what I'm dealing with right now. I'm not so afraid, just managing the hurt. Even if he came crawling back, I'd kick his sorry ass to touch. Jonny Wilkinson style. Ask me that a week ago, I'd have taken him back no questions asked.
Also get yourself a counsellor - just to talk to.
Putting my patronising head on: You're only 27 this is one of those lifetime learning experiences. I'm 42. My mother was 52 when she divorced. She's very happy now.