Dopamine is a chemical in the brain, commonly associated with motivation, goal-directed behaviours, and reward. Dopamine is also the cause for the sensation of 'novelty'. So, when you see someone you are in love with, and your brain presents heightened levels of dopamine, it makes your loved exciting on the brain. It seems special and unique, and a strong motivation towards him/her is created.
On the other hand, Norephinephrine is responsible for the extra surge or energy on your body. In a way, it is similar to the energy rush that adrenaline is responsible for. When your loved one is having an interaction with you, this chemical is released, causing you to feel a rush, you begin to get nervous maybe, or perhaps even anxious.
According to several antropologists, when these two chemicals are together, they produce "elation, intense energy, sleeplessness, craving, loss of appetite, and a very focused attention."
I hope this answer helps you, have a great day! :)
