If you can prove that you paid a large chunk of money into his account around the time he bought the house, and that you pay a standing order which covers half the mortgage and bills, and you have shared the house from the start, then you can argue at least that you have a claim to some of the equity, and arguably perhaps that it was a trust intending you to mutually own, I think - intention is demonstrated to share ownership. You need to see a solicitor, I'm afraid, but it isn't solely down to names on deeds. It is also down to intention to jointly own, and contributions in money or money's worth to the purchase price (deposit and mortgage).
Do you have any emails, texts, anything of that nature showing intention to jointly own? Did you search for houses together - were you at viewings together, did you both talk to estate agents? Get every scrap of paperwork you can together, and put it somewhere safe.
You can check the land registry online - it will tell you the named purchasers, and whether you are one of them. It's cheap and you can get an answer in 5 minutes from reading this. Anyone can get that info.
Given the amount of money involved I do think you should see a solicitor. Nobody here can give you a definite answer. Ask the CAB for a list of those locally offering free initial appointments - some still do.
If you aren't married, then your claim relies on the law of property. Thing is, you've effectively bought a house together and paid for it jointly. That gives you rights under the law even if you were just mates, or siblings. People confuse the situation where a SAHP hasn't ever paid anything, and the person paying had already bought before the SAHP moved in, which would entitle someone to nothing, with a situation like yours where you've split all costs down the middle with a clear intention to create a shared ownership.
I wouldn't agree to move out, but you need to see a solicitor sooner rather than later if you aren't on the deeds, as on the face of it he could change the locks tomorrow and you wouldn't have any way of getting back in.