Jesus has not yet returned and therefore "till all be fulfilled" has not happened.
You twist what Jesus said to fit your theology. Plain and simple.
In Matthew 5:18 Jesus was talking specifically about the Law. He was talking specifically about the fulfillment of the Law. He wasn’t talking about the end of time or His return or anything else. The “till all be fulfilled” was clearly in reference to the Law, and nothing else. And everything in the Law was fulfilled by Jesus.
It’s clear that you want to twist the “till all be fulfilled” into something other than what Jesus said in order for it to fit your theology. That’s your prerogative.
