My boyfriend of one year says that he's not sure if I'm the one he wants to marry?

I think what you're doing is exactly right, put a bit of space between the two of you and meet new people. It sounds like you two have done enough talking about it and what he needs to do now is some serious thinking. If after awhile, he still feels strongly about you not being the person he wants to marry, knock the relationship down a level and start dating new guys. There could be a perfect man out there for you that knows he'd want to marry you after the second he saw you and that's what you deserve.