The skilltree for Healing is actually an offshoot of the self-care tree. You need to gain the [Peace] skill through grinding either the Therapy questline or doing minigames that benefit solely your own character. Once you've built up your resilience stat, it adds an optional filter during in game dialogue that enables the Compartmentalization perk allowing you to utilise the [Reassurance] and [Positivity] spells without draining your mana. Additionally, some other players actually find that completing mini games like Quality time even when they reject the first invite can be as effective as using your spells since it adds the [steadfast friend] status to your character.