Don't feel like you have to rush to provide him with reassurance that you're going to be there for him regardless. He's already put you through hell worrying about when he's leaving, if he's leaving, what's gonna happen to the relationship if/when he leaves, etc. You gave him time to do his thing, and he needs to respect your need to create some breathing room in your mind. Now is the time when you get to decide if this is something you can really handle. Don't look at it as a "he might leave me if I take too long" kind of thing. Take this as a chance to rebuild some of your confidence and self-respect by commanding respect from him.