UK Citizenship if we Marry in the US?

Right now it's pretty certain my boyfriend and I are getting married sometime later this year, but it will have to be Stateside so he can be with me and work as I finish courses in America starting this September. (There was a change of plans, basically... I'll miss Scotland!  :\\\'()

Once we're officially a married couple, will I be able to live with him in Scotland again legally as his spouse, or will I have to apply for another visa?    And how do I become a dual citizen?

Yes you'll be able to come to Scotland even if you start your life in the US.  But you'll still need to get a spousal visa before you move over. 

As for citizenship, you'll have to live here for three years before you're eligible for that.