You don't have to be a rat, you just have to say NO.
My ex-dealer lives next door to me. It's hard, I know. Just the site of the person gets the wheels turning. that's why you MUST be strong in your recovery. Don't be a b*tch, or stir up trouble, just tell him you're no longer using. I highly doube he will respect that, but you must be firm.
I hate to say it, but it almost sounds like you might want to keep that line open (just in case).
Again, I don't know you or the situation, I just know from my own experience. It took months for me to finally tell my dealer I quit and that I did not want him to offer me dope.
When I first stopped using, I would just tell him I had no $$, or just not answer the phone. I honestly think, somewhere in my twisted addict mind, I wanted to keep that connection active, even if I wasn't using it. I finally got serious and told him, and then told him again (he continued to call, but I swear he was just doing that b/c his brain is fried and he forgot I wasn;t using.) So I told him again and again until he stopped calling.
I wish you all the best - I know it's hard. You CAN do this. Hel!, if I can, anybody can!
Much Love: SS