Placing a second name on a deed (house/land)?

I just purchased my first home. I took out the mortgage alone. I have a girlfriend, and we plan on marrying in the next couple years. She has agreed to split the mortgage and bills 50/50. Should I place her on the deed, in case of my death (since I have no other family surviving). But then I am concerned that if we divorce after a short time, she is entitled to my property while I am still paying the mortgage since it was borrowed in my name, in case she vacates the property and stops paying. How can I accomplish this. Can a lawyer draw up a contract stating "once mortgage is paid, house is split 50/50 and if there is a divorce she is only entitled to the cash that she has paid? I need a few suggestions?? (ps, I can make the payments on my own if we divorce) Thanks