Congratulations to you on your recovery time and on finding a life you are happy with!
I like what CO said. My own daughter told me she found "the one" pretty shortly after they got together...My own recovery helped me to keep my possible concerns to myself, but I thought it was a mature decision that they waited to get engaged and even better that they are waiting longer to get married. It gives them time to grow in their relationship. They live together too, and seem quite happy with what they have decided. I guess the key to me is that it is what they both are comfortable with so it eliminates the potential for one to resent the other down the road for pressuring to do things differently.
I personally think it is great that he is open and honest with you about his thoughts...Doesn't sound like he is waiting for you to fail...rather that he loves you enough to want you to have the time you need to focus just on you and recovery. I think it is awesome too that you want to understand and not rush to judgement!