Martha's goodbye to Clark/Philip on The Americans
Martha's goodbye to Clark/Philip on The Americans was heartbreaking, because even after everything she had been through, she still wanted him to be happy, to find someone else and live. She did decide she would do the same, but they had such a special relationship that seeing it end was quite gutting.
A Parting Shot on Agents of SHIELD
The spies' goodbye to Bobbi and Hunter on Agents of S.H.I.E.L.D. was so sad to watch. Seeing the crew gather and raise their drinks to their fellow fallen spies, without being able to interact with them, emphasized the pain each agent felt. Now that the spin-off isn't going through, hopefully Bobbi and Hunter return to the team that loves them.
Francis' Death on Reign
Francis' death on Reign took a toll on Mary and Catherine, and it was so hard to wath them try and get along without him. The way he went out, too. He'd miraculously survived his ear infection, but is then attacked in the woods and killed.
Kara's Guilt on Supergirl
Kara broke hearts on Supergirl after she was released from the control of the Red Kryptonite. The guilt broke her, and Melissa Benoist's acting was outstanding, as she was faced with the horrible acts she'd committed, and the people she hurt. All while dealing with the fact that she'd lost the trust of National City.
Lincoln Saying Goodbye to Daisy on Agents of SHIELD
Lincoln saying goodbye to Daisy was super sad. Watching Daisy beg her team to help her as she sobbed in agony was totally heartbreaking. Daisy was already trying to manage her guilt about being swayed by HIVE but having Lincoln pay for her mistakes destroyed her.
Laurel is Killed on Arrow
Laurel Lance's death on Arrow was shocking and unexpected. Her death was sudden, a last and lost plea to appease Damien Darhk's villainous plot and affect the Arrow squad. She left behind her grieving father and newly-alive sister. There went the driving force for keeping the Lance family together, but perhaps her death will do the same. Rest in Peace, Black Canary.