Seems to me that it could be sincere flirting, but he may just be trying to sort of create an work environment that mirrors his home life. I read in some psychology publication that our brain is wired to make every environment in which we spend a lot of time equivalent to a home/family. So in other words, the person in the cubicle next to you might subconsciously be viewed as your sibling, your coworker from marketing might subconsciously be viewed as your cousin, so on and so forth. What I'm getting at is that it may just be a way for him to create a "family" at work, and he may not even be aware of his different behavior towards you.
As far as advice though, I'd try to set up a conversation with him, and explain in mild terms how you feel like there's a difference between how he's treating others and how he's treating you. Depending on what his answer is, tell him that your not interested in a relationship with him, unless you are, and try to set up some boundaries.