Question

is true that lower boiling point i natural gas makes it more difficult separate?

Answer 1

cus i thought that higher boilings points make the bonds stronger....

Answer 2

Think about water, you have glass of water, you start boiling it, and if you leave it boiling, you're going to just have an empty pan with nothing.
Why?
Because the liquid water is becoming a gas, and where did it go? Into the atmosphere.
So no, boiling point does NOT make bonds stronger, it actually makes them weaker and hence, the intermolecular forces that hold water together are broken, as they become a gas.