Stefan and Caroline's relationship started with a crush, then a mentor, friends and now lovers. Since the beginning, Stefan caught Caroline’s eye, but he only had eyes for Elena. The life they lived made Caroline and Stefan became closer and closer each season.
They have always helped each other with the other's relationship problems. Caroline always supported his relationship with Elena up to the point where she developed romantic feelings for Stefan. Stefan comforted Caroline during the emotional fallout of her sleeping with Klaus. Stefan and Caroline share their secrets.
In Season Five, Stefan lost his memories due to a spell; Caroline was the only person that he trusted immediately and later told her she was "much hotter in person." After regaining his memories, Caroline got jealous when she thought Stefan and Elena were getting back together, which when she realized that her feeling for Stefan was stronger that she thought. Upon learning of Bonnie's death, Stefan told Caroline that he would always be there for her as she has always been there for him.
In Season Six, Stefan became aware that Caroline's feelings for him had turned romantic and made several attempts to reconcile, but their friendship remained strained. After her mother was diagnosed with cancer, Stefan stuck by Caroline through her grief, and they made up, and their friendship deepened, culminating in a kiss.
Stefan overcame the doubts in his mind and realized that he had developed deep feelings for Caroline referring to it as being potential "something even better" than his previous romances.
In Season Seven, Stefan and Caroline team up against a new threat in Mystic Falls, The Heretics and while boarding up Caroline's house, the two share a moment.
After being apart for three years, however, their relationship is tested being Stefan has been on the run with Valerie Tulle for three years. Caroline and Stefan bond and maintain a new friendship. Alaric and Caroline who started to date because she was carrying his children breaks up because he knows Caroline's heart belongs to Stefan. Caroline and Stefan talk, sharing a kiss together. Currently, Stefan and Caroline are dating once again. Shortly after this, Stefan proposes to Caroline, and she accepts his wedding proposal; they are engaged as of Season Eight.