What bothers Winston?

Well, what doesn't bother Winston is a better question. He is living in a dystopian hell. He is watched all the time, he feels sick and lives in a dirty flat. All the colour in everybody's life is gone. But, in an attempt to narrow down your question, he does begin writing a diary. This, of course, is completely illegal but it gives him some relief. Before he starts it, he wonders who he should write it to, "for the future, for the unborn". Winston doesn't know. So, besides living a life with all the soul sucked out of it, Winston in left wondering exactly who might read his small act of rebellion against the Party.

I hope this helps.