"As soon as I stepped into the terrace bar, I spotted her. She laughed at some joke the young man at her elbow was telling, and her teeth flashed in the candle-light."

Something about the way this is written already has me wondering why you don't tell us a bit more about who she is, right from the start. I think it might be the pronoun (her) in place of a name. Or, if the narrator doesn't know the name, then the pronoun is in place of something he does know about her. Maybe "I spotted the woman I've been waiting for all my life." or "I spotted the b**** who stole my heart." Whatever.

"People were milling around, the men mostly watching her, but I found spare seat at a table for one near the jazz-pianist. His soulful melodies drifted on the twilight air. I sipped my Cabernet while I waited."

You're missing an "a" between found and spare.

At this point, I'm noticing that you are bringing in a lot of descriptions but they are distracting because I still don't know anything about the woman, the narrator, or why we're there.

"I’d only had two sips when, like a tiny aviator returning from a perilous mission, I heard the drone of mosquito’s wings."

The use of this simile does seem overwritten to me. Also, since I had no idea what the simile referred to until the end of the sentence, I had to read it twice to figure it out.

" It landed on the back of my hand, its abdomen swollen with her blood. I nudged it towards the mole near my wrist.
It seemed drowsy and unresponsive, but it dutifully sank its proboscis through the dark flesh and deposited the blood into the "

Interesting...here's a hook

Of course, I have the advantage of having read the whole thing.

Your simile is misplaced--the way it's written, "like a tiny aviator" it would refer to "I", which doesn't make a lot of sense.