I've been in that same situation with a neighbour before. If you're able to you could talk to your neighbour (even via text) and ask that they help you by not bringing up cocaine in anyway and to FOR SURE not provide you with it. Any barriers that you can put up for yourself can be helpful. I find that if I specifically ask someone not to give me something that I would be less likely to ask for it cause just the idea of having to ask someone for something that I've explicitly told them not to give me makes me anxious, therefore less likely to ask for it. I dunno, that's just me though.