It depends on the people. Imho.. It depends on the depth of each relationship and the time requirements.
I was asked this recently.. I think.. for me there is a very real possibility of maintaining
primary, secondary and tertiary..
How that looks, or the logistics, to many variables to really narrow it down. I know I couldn't do two primaries. I don't have enough time in my day between work and life, to maintain that strong a time requirement with two people.