Really, love is complicated

"At first the female seems to show little interest, but gradually she will approach a nest hole where a male has displayed and perch nearby, or look in and out of the hole. Often the male will then enter the hole and may even sing softly while in the hole. The female usually leaves after a first visit, in which case the male continues his displays. She often approaches several boxes before she finally enters one. In the interludes between visits to nest holes she may also Wing-wave and give Song.

If she enters a nest hole while the male is also inside, this is a good sign that the two are paired. Following this she takes more of a lead around the nest site and is able to displace the male from any place that she flies to. She may be dominant over the male at this point."

Notes on Eastern Bluebird courtship from Stokes Nature Guides: A Guide to Bird Behavior, Volume 3, Donald and Lillian Stokes (Little, Brown and Company, 1989) 319.