I think that we don’t need to know he meets a sidekick unless he plays a major part in the movie.

Protagonist: Office worker
Antagonist: Drug dealer
Situation: wife died, revenge
Stakes: unknown.

You need to think of what’s at stakes if hero fails to kill the drug dealer. Then the logline will work. Just a regular vengeance is not enough – if hero kills the dealer – its good. If he fails? Movie wouldn’t be interesting if its just about “it works out or not.”

Another thing is that it was his gf’s choice to take drugs and dealer has no direct responsibility for her death – lets say, if dealer would refuse to supply his wife, she would probably find some other dealer.

So unless the dealer intentionally overdosed her, the protagonist’s agenda ain’t that strong.

When is his girlfriend killed by a local drug lord, former office worker takes justice into his hands, fulfilling his sacred vow to purge the city.

Even this one is not strong enough, we need some flaw of the protag. Image of office worker without a special skill masacring drug dealers is funny. And still you need to think of something that happens if hero’s fails in his journey

Or you can make this movie about hero’s inner path. How he become from former office worker into masacring killing machine – lost his inocence and during a movie, he must evaluate his moral values, deal with corrupted police, etc ….

Avenging death of his wife, former office worker turns into a killing machine, purging city of responsible drug dealers and corrupted police, unwillingly turning into a monster he once swore to kill.