I remember when I quit smoking crack. five months seemed an impossible goal. Oh my god. I never thought I'd be able to go longer than 4 days. It was painful and psychotic, and I didn't think I'd ever be able to quit. I got through it one day at a time.
I suggest you don't focus on the five months. Just say to yourself "Today, I will have no contact." and then give yourself the dignity of following through on your personal boundary.
Codependency is very similar to addiction. His neediness keeps sucking you back in. Like a craving for a drug. I guess that's why no contact is recommended. Being in contact with him isn't helping you and it isn't helping him either. He's still waiting for someone to save him. But he has to save himself.
That' the whole point. That's the only way it works.
He can't save you either. You have to do that.
Is there any way for me to not abandon him without getting totally codie?
You are not abandoning him. You are giving him the space and time he needs to get better. And you are giving yourself the same. Really, it's a gift for both of you.