Some stepparents become the person you call first. That isn’t disloyal to anybody.

Closeness is not a league table with limited places. A stepparent can turn into the person you call when something goes wrong, and that happens because of how they behaved over years rather than because anybody got demoted. No rule in a family says affection has to go in order of arrival. Guilt about it is common, and it is not a sign you did anything wrong.

If somebody has quietly become that person for you, you might let them know, in a plain sentence rather than a speech. You can do it without comparing them to anyone. Nobody has to be told where they rank.