First of all- Only you know him well and what he is capable of doing. Do you think he would start trouble with you right before leaving town or do you think he just wants to say his last goodbyes? If so, it could mean closure for you and him.
Secondly- Does this gay friend of yours have any feelings towards you what-so-ever? Be honest with yourself. If she does, than it wouldn't be wise to go into a business deal with her because if any bad blood stirs up it will seem like a divorce where you could cut the air with a knife. In my past experiences, living with someone else has been a sure way of ruining a friendship. But maybe you two really work well together and it would be great. Have you tried living together first for a trial run at it? See what happens!