This male is lucky; most never get to mate. The female will now stock up on nectar and eventually find a place underground to hibernate in for the winter. Here's what the Bumblebee Conservation Trust tell me will happen after she wakes up next spring:
When she has chosen a nest the queen will begin to collect pollen from flowers, to bring back to the nest. She forms a mound of pollen and wax (which she secretes from her body) and lays her first brood of eggs. She also collects nectar which she stores in a pot-shaped structure made of wax which is positioned in front of her mound. The queen keeps the eggs warm by sitting on her wax ‘nest’ and shivering her muscles to keep warm. Sipping from the nectar-pot gives her enough energy to incubate the eggs for several days until little white grub-like larvae emerge. These larvae are fed on pollen and nectar which the queen goes back and forth to collect from nearby flowers. Once they have eaten enough, after around two weeks, they spin a cocoon, inside which they develop into adult bees.
They key factor in all of this, obviously, is flowers, and that's where bumblebees need our help. Click here to read about how you can do your bit to make your garden bee-friendly.