My first "reaction" is that if you grip nr1 to move the end meeting nr2, then why not just grip both lines and move the common endpoint, or use stretch?
Other than that, you would have to set up a reactor as well as store some identifier in nr1 to identify nr2, and perhaps both if you want nr1 to react to nr2. Bear in mind that the reactor requires the software loaded to have the reaction. Meaning if the drawing is opened by someone who doesn't have the reactor loaded, then a reaction can not take place.
