Hi freefalling !! you deserve much more than this, hopefully this will be over soon.
He did not "replace" you, his addiction needs enablers, that's all.
You cannot be replaced and the world would be less if you were not around. I know you already know this but wanted to mention it out loud
Getting someone else right away is common MO for alkies I gather, and for normies as well, at least in my view. My opinion is that people that do that are emotionally weak and unconsciously are still looking for Mom or Dad; not a real equal partner.
Someone healthier can be alone for great lengths of time, is independent and has gone beyond that stage. It is very sad, in the end. Life always shows you your lessons and there is no one else ever,that will "fix" someone else.
Goods news is that there is a life huge of blessings for you.
Hugs from Mexico
Tc999