The out-of-universe reason for Ben and Julie breaking up was that the crew wanted to do something different, and some of the producers didnt care for their relationship in Alien Force and Ultimate Alien.

What happens to Julie in Felicity?

After a while they seem to be on different paths and Julie ends things with Ben, after which she learns he cheated on her with Felicity. After some estrangement they eventually manage to become friends again, and always have a close bond due to their history.

Can Gwen Tennyson fly?

Charm of Telekinesis: This charm greatly enhances Gwens telekinesis as well as grants her the ability to fly freely.