Advice Please? Addicts Dating

what are peoples opinions of 2 addicts dating? 2 people who have used for months together are now clean than use than get clean and the cycle continues. Why has it been many months like this? Basically my ex BF who is a heroin addict left me for a girl he met in rehab 9 months ago. I STILL feel like he will be back but he says he loves her and claims to have 5 months sober. What am I supposed to think? Does he love her? I was the best to him thru his many relapses and episodes where he went missing to get drugs and now he treats me like beyond crap and I'm not an addict just stayed with him for many years thru this and he left. I love him more than anyone in this entire world? Is their anyone with a similar story? I'm lost and confused.
I am with an addict now. But one thing my sister told me is if he gets sober and decides you are not what he wants then you have to be ok with that. He is still with me, but I'm not sure its what I want anymore. Its hard to date an addict or even an addict in recovery. But honestly i would move on if I were you. Yes you were happy, but that is not what it is now.