Interesting premise as it has many layers of sub plots that reflect on each other. The MC being a drug addict seeking redemption is a tricky character as the story will have to work extra hard to justify empathy but seeing as his goal is to save a girl from the same life he has the story has a built in empathy generator.

It would help a lot if the MC’s journey to quit could be directly related to him stopping the girl either that or if the MC would find himself facing a choice of self sacrifice in order to help the girl.

As it stands the logline is missing the starting point what was the inciting incident for him to help the girl?

Also the logline needs leaning up perhaps:
After a drug addicted teacher discovers one of his student injecting heroin he must stop her from ruining her life despite her father being her dealer.

The father character as the antagonist needs more clarification, than I gave in the example above, in his relation to the plot and type of antagonist but this is the structure and length I was referring to.

Hope this helps.

Agreed with Peter.

It isn’t clear if this is a comedy or drama so best to re draft the logline with that in mind. Also better to specify a main character and perhaps pin him or her up against their siblings in the journey. Otherwise it is hard to picture how the main action of the film will play out.

Hope this helps.