@pox22: Hey there. First up: congratulations. I'm a recent master's graduate [medieval studies, in case you're wondering] and I know what it feels like when an academic superior takes a personal interest in you and your future career. Nice one!
I understand that significant change can be intimidating and that you would likely be committing to a long period of time away from home. Leaving family and friends behind might be tough, but I think in this day and age you will be able to keep in touch with the people who really matter to you, not to mention you will be surrounded by like-minded people if you do get onto that programme and should have no problem making new connections. I live in the UK and have recently applied to PhD programmes at a few US colleges, a much bigger move than the one you are considering. To my eyes your situation is not a dilemma: it is literally my goal. I would encourage you to grab the opportunity with both hands. You write with such reverence for the very idea of studying at BU that I can't help but suspect you already know it's what you want to do.