Remember Kelly´s Heros? Stop with the negative waves...... Of course there can be disagreements, and of course these can sour some relationships, which is why a clear agreement is needed at the outset.
One hears mostly about the sharing gone wrong, but lots of flying clubs and partnerships exist and work out. Like maybe 50% of marriages end in divorce and some terrible, but there are another 50% that carry on.
...and there are in fact car-sharing schemes in many major cities, as well as sharing of summer houses, ski chalets, sail boats....even wives! So if the schedule fits, it can be to mutual benefit. If it looks like they will conflict at the get-go, then that is not the "right" person to share.
Cut out the negative waves, Moriarity.....