Last Thursday I jumped up onto a ledge at the office to take better pictures of the vaulted ceiling. We're renting out the space so my boss asked me to take pictures.
My gf and I bought a house. The mortgage is 50/50, as we both own the house. All the other costs are divided according to our pay. I earn a bit more than she does so I take about 60 percent and she about 40.
Of course your situation is a bit different seeing as how you would be paying off your mortgage, so you could do the mortgage according to pay as well or smth. The important bit is you figure out something you are both comfortable with to prevent any resentment in the future.
Ricin was used in Breaking Bad. Fairly easy to produce and administer.