Gravity

I can't stop thinking about gravity.

General relativity says that gravity is the same thing as acceleration. If so, then acceleration bends spacetime and inertia seems to be the resistance of spacetime to being bent.

But gravity and inertia are equal. We know this because a pendulum's period depends only on its length and not even one whisker on its mass.

How is it that two different things, bending spacetime and resistance to bending spacetime, are precisely the same? They can't be. They must be the same thing. Gravity must also be resistance to bending spacetime. But what does that even mean?

Photons do not bend spacetime because they have no inertia/gravity. A photon approaching a mass doesn't bend towards the mass like a particle would, it follows bent spacetime around it. Why?

Please clarify in the comments below.