If you aren't married then I'd advise you to get something called a pre-purchase agreement. If the deposit is being paid by your parents or her parents its going to get halved down the middle if you don't have a ppa. Remember though, your lender will have to agree to this or you could end up in deep water when/if it all goes pete-tongue.
This is an appropriate site to have a look at
https://andersonstrathern.co.uk/news...ase-agreement/