Erin Nyx Rosier is a Gryffindor one, Draco never notice her even she always with Harry, Ron and Hermione until Draco saw her with Harry. Her relationship with Harry will be her own rollercoaster when Draco meddle on it.
Harry and Draco are in a quite new relationship and have never really gone further than snogging... yeah, you see the problem, two boys, both 18, but with minds of 15 year olds.
Anyway, Harry and Draco starts to consider going further in their relationship but is a bit unsure whether to ask each other about it or just go for it... So why not just start tease the other and see where it goes.