Separation (The New Beginning Series, Book S...
Alex has taken an unexpected turn.
Yes, she is in pain from losing Bonnie and Damon, and Stefan has left without saying goodbye, but she is finally attending Whitmore College as a form of distraction, and she is rooming with Elena. They are trying to get past the Petrova Curse, and with the lights of recent events, it's not necessarily the first thing on their minds.
Everyone is grieving in their own ways, including Alex.
She is mad at Stefan for leaving the way he did, yes, but she is also still in love with him, and with a love like Stalex's, you can't be angry at the other half forever.