in practice it wouldn't be realistic to expect a single person to share his attention/interest equally among n people, if n became too high.

If n is >10, then even with someone devoting all their time to relationships, they are still going to be giving a small amount. to each

For n=1; the relationship will generally be saturated before all the time is used up, but for higher values of n it becomes more and more likely that all the time will be used up, before the relationship is saturated.

Personally I couldn't handle more than 3 primary relationships, and I wouldn't even be able to handle 3 unless the partners also had other partners; to be there for them when I am otherwise engaged.