Shadow..

Sonic fell in love. For the first time in his life, he felt something so powerful he couldn't get it out of his head. His attention always returned to one person—Shadow. For Sonic, he wasn't just a rival or a friend. Shadow became the one who understood him better than anyone, the one with whom Sonic felt truly himself. With each passing day, his feelings grew stronger, evolving from mere affection into something much more.

But Shadow didn't reciprocate his feelings. He didn't understand his own feelings, wasn't ready to accept Sonic's strong affection, and chose to keep his distance. This was a real blow to Sonic. He couldn't understand why the person he loved with all his heart didn't feel the same.

Over time, Sonic's love turned into an obsession. He began seeking out Shadow too often, constantly thinking about him and noticing every little detail about him. He wanted to be close to him more and more, wanted Shadow to look only at him. In public, Sonic remained the same—the cheerful, kind, and energetic hero everyone knew. But alone with Shadow, he became different: overly emotional, overly attached, and overly open with his feelings. He constantly spoke of his love, made no secret of his jealousy, and became increasingly afraid of losing Shadow. He pestered Shadow, sought him out everywhere, and overall became obsessed.
None of Sonic's friends noticed what was happening to him. To Tails, Amy, Knuckles, and Rouge, he was still the same Sonic. Only Shadow saw how much his rival had changed.