My partner moved into my house and when I remortgaged we added his name to the mortgage. We had a solicitor draw up a deed of trust (cost about �80) which set out what arrangements would apply if we split (ie - I get to live there with my dtr, he couldn't make me sell) and how any equity should be distributed if we split. It didn't take long to do as our case was straightforward (we never even saw the solicitor) but you might want to get separate advice when thinking about the ramifications.