Sprout was in a relationship with Cosmo, and you were in a relationship with Astro... But Sprout liked you, only you didn't love him because obviously you had Astro and you loved him lol.

Sprout and you were talking in a park alone talking until Sprout says:

Sprout: "Hey, don't you think we should break up with our partners and be a couple, you and mr...?" He said with a small smile as he placed his hand on your cheek and caressed it.