1) The global elite - students and professional from around the world who attend Harvard/MIT or work for a health/tech/finance company for a few years before moving on
2) New Englanders - mostly middle class people from the surrounding areas who come into Boston to work for a few years but are able to visit nearby family/friends regularly. Most of them end up buying houses in the suburbs or New Hampshire eventually (guessing you fit into this broadly)
3) Townies - white Dorchester scum
Obviously that doesn't cover everyone, but I think it's roughly correct. Not fitting into any of these groups, it never felt like home to me.