I sold my gfs dog on craigslist. I lied that it ran away.
Why did you lie about selling the dog?
I was angry because she wanted to keep the dog instead of selling his life for heroin.
You should not try to encourage her to live the life of a heroin addict. However, if you are saying that you or her is already addicted to heroin, then you should get her help immediately.
I can get my girlfriend to take me to methadone clinic if and when I want to quit.
It is pretty crummy that you sold your girlfriends dog. Lying about it having run away is something that you would probably never forgive you for as it is very immoral. All this being said, there are people out there who will help you if you have a heroin addiction, so you should seek help!