That explains a lot. Gin and Sherry might have had a romantic relationship, but because Sherry dumped him, and Sherry betrayed the organization, he is chasing after Sherry not only because she betrayed the organization, but also because he is angry at her for dumping him. That explains why he is trying hard to catch her. Not to mention, Vermouth likes Gin, and is jealous. When she realized Conan and Ai may be a good couple, she stopped chasing after her. (Honestly, I never wanted Gin and my beautiful Sherry to have a relationship.)