just completed taking independence, now preston won't follow me anymore. Anyone know what needs to happen to fix this, is it normal game progression or a bug?

Well, I answered my own question, Preston was bugged. I loaded the last save I had that was before the mission taking independence, unfortunately it was 3 hours before I did the mission, (need to save more often, lesson learned). I did the mission again, tried a different tactic for the mission (in the off chance that mattered) and afterwards Preston would follow me again.