I'm doing a bow/healer nightblade that feels pretty powerful. I'm not that familiar with templar, but I don't think you have any CC slotted. Swapping out venom for magnum shot would let you kite enemies better probably.

Also, one of the best parts of using a bow is the easy crits from stealth. That and make sure you don't fire your arrows by releasing the mouse button but by using a skill so your effective dps is doubled with attacks and abilities happening in quick succession.

Failing that, you could try casting a regen on yourself before starting any combat. On my healer I keep all my heals on the same bar, cause I'm not templar ofc, but my ability set-up goes like this:

bow : magnum shot > killer's blade > swallow soul > healing path > shadow disguise

staff : illustrious healing > regen > silver bolts > ward ally > siphoning strikes

anytime i'm in trouble i can pop shadow disguise which overcaps me on armor and spell res. when i solo I just use the bow bar, the passive healing from path, blade, and swallow soul keeps me at full 98% of the time and when i group i mainly use staff with siphoning strikes keeping my mana bar full enough to constantly spam healing spells like mad. it works pretty well.