My best advice on how to draft the lease/option to purchase is to assume that you two will have a horrible breakup 2 weeks after signing the papers and draft the papers to cover that contingency. Be fair, but address potential problems. OTOH, don't spend all your time focusing on the possible negatives - you might get so bogged down that you lose sight of the goal - to rent/sell your friend the condo.
Use a real estate broker for the actual sale. When 2 non-brokers sell a house, problems often arise because neither knows the relevant state laws on disclosure, deeds, inspections, escrow, contracts for sale, title insurance, etc. If the 6% commission seems too high, talk to a real estate lawyer. View the commission/laywer fees as an advanced insurance policy. Even if you have no problems with your friend, the deed you draw up may put you on the hook to the people HE sells the place to eventually.
Note: you cannot make the lease/option contingent on your continued relationship. That's too close to an unenforceable contract for sex (the reduced rent represents the 'fee'). You may find that you can't enforce the contract terms!
Even if you've already signed the papers, you two can go back and amend the contracts to reflect your new agreements.
Good luck,
Tracey
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.