The two share a strong rapport. As a Caster, Maggie was probably always aware of Sizemore's "Rock Star" status in the Magic Kingdom. However, they probably weren't all that close until they linked to uncroak the Volcano, and learned just how compatible they really were.
Some level of romantic involvement is implied, but not yet resolved as definitely present or absent.
Sizemore and Maggie have discovered that they can easily link up for casting spells together. This linkage not only boosts Sizemore's abilities, it is also very enjoyable.