You say that he's only 23?
Well, most 23 year olds aren't ready to make life committments and they are still questioning what, where, with who and how they want to spend the rest of their lives. Most 23 year olds are still trying to "find themselves" so to speak. So, I think that is why he questions his relationship with you. Being involved with an older woman with three kids can be overwhelming to someone his age. I would proceed in this relationship with caution. It may not last and I don't think you can really count on it. I'm not saying to break up but you may want to consider it more of a dating relationship rather than something that will be a life long committment right now. It could develop into the committment that you seek, but, it has only been 8 months. That is not that long.