If you decide to live with someone, there's a lot to think about. You two may click together better than the last person he lived with, but he may also be thinking about his personal space/time. I couldn't even begin to guess at his reasons, but that's one that comes to mind for me. It's a big thing to move in with someone, because if you already have problems, they become amplified, and it's harder to get away from them when you need time to sort out your thoughts. Just remember if you do move in together that the bumps in the road will happen.
I hope that you guys can get along and that it's not too stressful for you. There is a difference between dominance and assertiveness, because assertiveness is just knowing what you want to communicate and being firm about it. Think of it as being clear about yourself, and helping the other person not to have any doubts.
I also hope you feel better soon, health-wise. :( It's good to see you around again, I had wondered why you disappeared.