My blood ran cold when I read this OP, I was in exactly the same position as you some years ago. We purchased a house I paid a sizeable deposit, (funds from what my father had left me in his will). This property also needed doing work on it (a lot of work, I may add) 3 years in and just the end was in sight. It wasn't though, I found out about his affair.
My stupidity was the belief that we were 'solid' even when my solicitor asked if I wanted to protect my 'assets' I remember feeling insulted as could never see us splitting up. How very naive I was.
I ended up starting all over again, he moved the other woman into the house and I lost virtually everything. I found the cheapest place I could afford and scraped together a deposit. I moved into my little house with my two cats, my bed, and a few belongings.
What I lost though cannot compare with what I gained. He controlled me (awfully but again you sometimes don't see it or want to admit it). I got my life back, and live it on my terms.
OP, please seek legal advice urgently, do not be me, the doormat that I was. We put our trust into our partners, thinking we are both on the same page, however that can change in a heartbeat (in my case when the grass looked greener for him).
Good luck and I am so very sorry this has happened to you 