I guess to me, it's somewhat irrelevant whether it is or isn't biological.
I, personally, have had crushes on multiple people more than once and figured everyone does or could, given the right two (or three) people coming along. It's interesting to me to read that some people have never felt that way.
But I guess I see that as feelings, and monogamy as a choice of behavior. My feeling is that it's really beside the point if I have ever loved two or more at once or if someone else never has. I've never believed we need to act on all our feelings.
So, as I said, to me it's totally irrelevant whether monogamy is biological or not.