I am what you cannot be but you once were what i will become i am what only blind can see and of infinity and 1 i am the sum i am the cure and i am the cancer?

After hours of trying to figure this out...

A thought.

I am what you cannot be but you once were what I will become.

We cannot be an idea, but we were once an idea from our parents. We are now trying to think of the answer, therefore a thought.

I am what only blind can see and of infinity and 1 i am the sum.

Only blind men can see their own thoughts, and there is no greater number than infininity, therefore that is only a thought.

I am the cure and I am the cancer.

The riddle is the answer is the riddle is the answer.

We are trying to think of the answer to which the answer is our thinking.