Your inside world decided your outsidener self dictates your behavior.

Do you know those people who live painfullyanyone who lives with pain?

I cannot help you translate exactly what you are trying to say, but using the word "pain" here implies a physical sensation, not an emotion. You could say that some people live with regret, guilt, sadness, misery, grief, etc.

Doesn’t their pain come from their inner confusion?

Yes, it’s iIndeed thit is.

We all intend to change ourselves by changing the environment.

But we should think itn reverse, w. We should change ourselves first before changing the environment.

Your inside world decideds your outside behavior.

Ordinarily, "your outside behavior" would mean e.g. outside the house. But as it stands, this is a reasonable metaphor.

Do you know those people who live painfully?

"live painfully" would be smoother as "live a painful existence".

Doesn’t their pain come from their inner confusion?

While this is grammatical, it's weird to ask yourself a question and answer it in English. English has rhetorical questions, but we don't answer them.

Yes, it’s indeed thiit does.

We all intend to change ourselves by changing the environment.

This is grammatically correct, but it's a random change of topic from "inside world" (our personality, our metabolism, etc.) to "the environment" (plants, the ocean, the sky, etc.). Maybe it should say "our environment" (e.g. our living conditions)?

But think it reconversely, we should change ourselves first before changing the environment.

Again, it's grammatical, but is somewhat illogical. When we "change ourselves", we are referring to our individual personality and body. When we "change the environment", we might be planting trees, picking up litter, etc.