Don't be too hasty, kate.
(i) properly set up, it might give you a nice supplementary income, especially if it is a nice flat in a des res area - i.e. don't rent to a friend casually but set it up properly....perhaps use an agency to help take some of the weight off re checking folk out, contracts, etc etc etc.
(ii) it provides you with security
(iii) it provides you with a base if something goes wrong with your relationship (hopefully not) and it means your eggs are not in one basket....