The next manga to look into is Gundam Wing: Ground Zero. It is the most unofficial work to be looked into so far, but it doesn't hurt to look. While Catherine doesn't appear in it, at the end of the Third Issue, Heero thinks,
"And even though we won't have weapons... There are still people we want to protect. So it's our job to get stronger."
While this is being thought, it shows the Gundam boys at the places they belong to now. Trowa is shown in front of a lion's cage. In all indications the people he wants to protect the most is at the circus. Readers can think his main objective is in protecting Catherine.
Despite that, there are no romantic inclinations for fans of such a pairing to grasp onto. All it indicates is that those at the circus are important to him.