Well, you can't expect flowers to last forever! They have to die off
sometime and the browning of the flower heads indicates that this is
happening - it's all perfectly natural. As for the ants; they will
swarm over any plant that is infested with aphids or other sap-sucking
insects since these secrete considerable quantities of sugary liquids,
which the ants love. Helichrysum italicum ssp. serotinum (curry
plant) tends to attract aphids, which colonise shoot tips and flower
stems and may have even been placed there by the ants. Now the
flowers of your 'curry plant' are over, you might as well give it a
good trim - cutting back the flower stems and shoots to encourage a
good bushy habit. Then drench with an insecticide or weak solution of
washing up liquid to get rid of the aphids.