The aquarium is a little isolated from date-type spots. Fells for example is like a mile away.

Something like the Walters Art Gallery has a bunch of vibe-y spots a short walk away. Ceremony or Dooby's for coffee. Sugarvale or Topside for drinks. Allora or Dooby's for lunch. Helmand or Brewer's Art for dinner. And you could peek your head into the Peabody Library or climb up the monument while you're there.