Hi Gem, thank you for your post. I have been in the same situation, right now.. In a relationship with my addict ex boyfriend for 2 years, now 7 weeks of no contact and he also did replace me by new girl. I know that he took the girl for his brother's baby christening - where I was invited initially before I broke up with him and where I was supposed to meet the rest of his family! The girl is blond, Barbie - looking and lots of makeup. Quite different from me.
It hurts me a lot because this was supposed to be our fresh start after he moved away. Anyway, I broke up with him because his posts on Facebook were highly insulting to me. Posts type of "how great his life is since he moved out and that new people he met are amazing". I felt bad, because I helped him for 8 months while he keeps relapsing and then everyone new was amazing. Anyway, even after those posts (and there were many), he wanted me to come over.
I find really helpful your post and all the responses here. I told myself that you never know what is really going on in that relationship and honestly I don't believe that the girl will get happy ending with recovering addict/alcoholic who didn't take much time on his own to recover.
Take care and I hope that it helps you to know that you are not alone. You work on yourself and you will be good soon. While he will repeat the same pattern over and over. Take care x