I like this card, 1 resource for 1 extra health and sanity, that's a fantastic conversion of resources.
Sadly, liking cards isn't the same as them being good. First off, Dodge exists, a card that costs the same amount of resources and is very likely to net you the same amount of damage sustained or more. Take for example the core set campaign, Dodge immediately has superior payoff if you save it for the confrontation with Ghoul Priest, not every scenario has such a good example but most will present you with some route to preventing 2+ points of horror/damage.
Perhaps the most important benefit in Trusted's favor is that it also protects against treacheries, but that strength is moot against the fact that it has the added clause of needing an ally target, not to mention that allies might not stick around long enough for you play Trusted on them in the first place while Dodge is fast.
Should you play Trusted? Yes, try it. Keep in mind however that it should only be played in an ally heavy deck with more ally-support cards like Charisma, Inspiring Presence and especially Calling in Favors, it happens that Trusted helps your allies stick around and those other cards all depend on allies sticking around until you get an opportunity to heal them, swap them around or fill your board with them.
In summary: Play Trusted as a mechanic to fortify your allies to then combo them with Ally based mechanics. An extra shot with Beat Cop, an extra trigger on Aquinnah. An extra bite from your Guard Dog. Extra tank on your Art Student before you Calling in Favors on them and replay them.