A smidge late to the party, but the Battle of Fort Ticonderoga was "fought" on May 10th, 1775 and its victory enabled the Siege of Boston to happen. "Fought" in quotations because it was a route with no shots fired and an unconditional surrender by British forces to American Continentals. Ticonderoga's cannons were stripped and sent through an overland route to the bluffs overlooking Charlestown and Boston, forcing the British to surrender in early 1776.
The expedition was led by Ethan Allen and Benedict Arnold but among its officers was also future members of the 2nd Light. Namely Elisha Sheldon and Samuel Blackden under David Wooster's command. Following the Battle of Lexington and Concord, a call to arms was taken up by various militia and the Cause was a rallying cry to encircle the British defenses at Boston. Most of the militia went to Boston, but some went up to Ticonderoga knowing that they needed cannons to force the British to surrender or to drive them out of the city themselves. The British had their warships with cannons able to be fired up to Continental defenses, the Continentals could not fire back.
After this, Sheldon was placed in command of the Light Horse regiment from Connecticut, serving in Boston and then down to New York City and part of the Battle of White Plains. Blackden's command was unknown, but the two would eventually meet and serve again with one another when the 2nd Light was raised.
Based on the cordial nature of Sheldon and Blackden's letters to each other and to others referencing the other; along with the fact that both came from Connecticut, we can infer that both were friendly with one another enough to serve in the same regiment at the re-organization of the military in early 1777 (the formation of the 2nd Continental Light Dragoons). However, both also had their pride and judging by the nature of Blackden's lack of resignation, but refusal to actually do his duties as 2IC after the disastrous letter sent to Sheldon by a majority commissioned officers in late 1778, the friendship was broken.
One cannot truly know why, but perhaps Blackden compared a lot of Sheldon's indifference and indecisiveness in his response/lack of response to the letter to the early campaigns - where merit and glory in the battlefield mattered a lot to gentleman officers. Maybe there was something Blackden saw in Sheldon that he compared to Arnold from Ticonderoga campaign. Maybe it was something else. Whatever it was - Sheldon and Blackden knew each other from 1775 and to see such a friendship broken by mid-war is truly disappointing.