Yes. As long as you do not share a biological grandparent, it is legal in all states to date as well as to marry. There is also almost no risk of genetic problems if you had children.
There is no reason why you couldn't date, especially since you're not blood-related, but since such a thing is frowned up in our society, both of you should be wary of family's reaction.
It is usually a risky affair to date a relative however distant.This is due to the fact that no one can ascertain that there are not genetic connections.You would be risking to have children with abnormalities and other problems.It would be prudent not to date given the tight position you might fall into medically.
