Gu means darkness and ru means light so guru is anything that brings us from darkness to light.
No experience or thing or relationship has the inherent power to bring us from darkness to light, but WE have the power to use every experience, thing or relationship as the bridge that takes us from darkness, or illusion, to light, or truth.
That power lies in our asking to see everything and everyone through the eyes of the Holy Spirit (true Self) rather than the blindness of the ego (made up self). Which includes brutal self honesty and willingness to admit that we don’t know what we see, or what the world is, or what anything is for.
Once we ask for everything we see to be reinterpreted for us, and truly stay determined to that process, the light will start to dispel the darkness.
In my experience, there is no other way out of this self imposed suffering we mistake for life. But as soon as we truly ask for a better way, the light will step in to guide us. And everything and everyone becomes our guru.