Remember the old saying- Never mix business with pleasure...
Dating a co-worker, especially a boss, is a virtual minefield. Others at work will likely think you are getting special favors from him at work, and if the relationship doesn't work out, there will almost certainly be conflict there. It's easy to say neither of you want anything serious and you can back out if it gets too serious, but that's when it is most difficult to leave a relationship, and one or both of you are likely to develop feelings for the other one...