Wanting to purchase a house with fiance and 1 friend....need advice

[Cathma]

I am looking to purchase a house with my fiance and 1 of our mutual friends. Is this a bad idea? I need to know what I should do to protect myself from losing money and doing this the right way. Do i make a contract?? I am confused as to how this will work, if the friend decides to move out and we have to buy her out. I will be the only one putting up the down payment, so am a little concerned over this also. I am anxious to hear some advice from people outside the family.... Thanks so much!!