Thanks for your question.
Obviously, for security it is best that you are both named on the title to your property, this is the key. A person who is not named but who pays the mortgage is very poorly positioned. This can only be done if either there is no mortgage on the property OR you remortgage from your sole name in to your joint names (for which you would need the lender's consent).
So, he could either pay of the mortgage or you could both remortgage with perhaps him paying off some of it (or none of it)
If you are both to be named on the title to the property (ie. In either of the above ways) your conveyancer will likely recommend that you hold your interest in the property as tenants in common. This means that your respective interests pass according to your will (ie. not automatically passing to the surviving owner) and that you can own unequal shares in the property.
You may then make a declaration of trust, which is a deed sworn by you both in which you specify how the proceeds of sale of the property (ie. when it is eventually sold) are to be divided. This would define the percentage interests each party has in the proceeds of sale and thus reflect each party's contribution.
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