Trust is the Blue Bubbles, yes. Honestly, the easiest way to raise characters' Trust is to just grind up a shit ton of gems, and then repeatedly buy the +Trust item in the shop. There's no way to track trust like there is the Affection (how filled in the Heart icon is is the tracker for affection, but just giving 5 of the +Trust item to each party member who is proving annoying under AI control should be enough to get them all under manual direction.)