unequal co ownership help please

[Matthew Nielson]

Desperate need of help on understanding how to make a fair agreement for the both of us.

some details:

buying a fixer upper home with some immediate concerns. 

I am putting $41,000 down payment on the home, covering inspections, and closing costs.I also expect to spend $20,000 right off the bat to do some repairs on the property. 

partner is not able to contribute to the down payment , closing costs, or initial repairs. 

we calculated the monthly expenses including mortgage, power, gas, taxes and figured out that my partner can afford to cover 35% of those expenses. I will cover the other 65% of the expenses. 

However any home improvements, major repairs, unexpected costs etc will be covered 100% by me

we had planned to take the tittle as tenants in common with a 65/35 ownership split. however this will not protect the investments I will be making into the property over time that will not be matched by my partner. 

we will be getting a cohabitation agreement as well. however I am still at a loss for what a fair way to split the equity in the home will be in the case of a split and sale/buyout on the property. obviously I will have invested much more than 65% of the home expenses. but there is no way to know for certain what % of the expenses I will have covered at any point in time. any advice at all in how to fairly split the home in the event of a split/sale/buy out would be greatly apreciated.