“Healing” is needed; “a healer” is not
Some characters in D&D 5 are squarely “healers” (e.g., Life domain clerics) while others are characters who can heal. After you progress a little in your game, your ranger could be one of the second type.
The situation you describe where the party is nearly wiped out on one of their first outings is not so unusual for low-level D&D 5e. A few lucky/unlucky rolls can swing things in favor of the enemy, and your party might not have many resources to recover from the bad luck.
But you don’t have to rely on lucky death saves, even without a healer.
Be an archer…who can heal
Since you wish to focus on longbow instead of using spells in combat, that frees up your character to use the spells for healing. This can be a good combination — since you are not charging into melee, your ranger should have more opportunity to move around the battlefield and heal allies as needed.
Cure Wounds and Goodberry
At second level, your ranger will have access to 2 good healing spells, Cure Wounds and Goodberry. Cure Wounds is definitely the spell for keeping someone in a fight a little longer, but don’t overlook Goodberry — it gives you the ability to revive dying characters (ones with zero HP) ten times. Plus, if the healer spell caster gets downed after casting the spell, someone else can administer a remaining Goodberry to them.
Buy Healer's Kits
It’s easily overlooked how useful Healer's Kits are — they let you automatically succeed at stabilizing a creature, even if you don’t have the Medicine skill, and they cost only 5 GP — that’s 5 SP per use. (See PH p. 151)
The Medicine Skill
It would be handy if someone in your party, ideally someone with a good Wisdom score, had the Medicine skill (even though Healer’s kits are a good substitute, when they are available). You might be off the hook for this one, as it’s not a Ranger class skill.
Since you are just starting out with D&D 5e, the players might ask the DM if they can switch out an existing skill to be proficient with Medicine.
Healing options as you progress
Once you progress a couple levels, the 50 GP price tag on healing potions will be less of an impediment for emergency healing.
The Healer feat is also a great option for a character of any class.
If nobody has the Medicine skill, the Skilled feat can make that available during level progression. Nature and/or Survival might also be useful for this if your DM is on board (see Ranger Powers below).
You might talk to your DM about leveraging your Survival and/or Nature skills, and maybe your favored terrain, to find herbs and natural materials to craft Healer’s kits, potions of healing, or even custom healing items.
The rules for downtime activities (in the DMG) are open-ended, so be ready to persuade a reluctant DM. You can mention that rangers in LOTR knew about the healing powers of herbs and plants. Don’t be adversarial, you are trying to find a way to have a workable party while everyone can still play a character they enjoy.