it seems like your putting significance on insignificant things. After two hours maybe she was just done hanging out, and for went the cigarette to get some alone time before bed.
if she lives with her parents maybe she doesn't get that a lot, and with finals and now a boyfriend she might just need time for herself.
In those cases... Make sure she's alright. Wish her luck in her stressful endeavors. Tell her she can call if she needs to, and be on your way.
Ted, how do I explain this to you. Last night, I ate the best cake of my life. Do you think I'm gonna let that cake out of my life? Hell no. I'm gonna find out what bakery made that cake and I'm gonna get some more cake.