90 days is a drop in the bucket. Literally. It takes at least a year for the human brain to even heal from the dopamine scorching it receives during years and years of active drinking.
What your boyfriend is up against is a full lifetime of committing to and staying committed to full recovery. And that will have to come first in his life. Make no mistake about that. His recovery will have to come before you, before any children you may have together, before any career he may have. Are you ready to be all in with that? Because that is exactly what you're looking at.