2. Kevin Durant
The Golden State Warriors hit the free agency jackpot in 2016, when their long-term planning, Stephen Curry's bargain of a contract and a skyrocketing salary cap allowed a title contender to sign one of the 15 greatest players in NBA history.
Kevin Durant joined the team and the Warriors were unsurprisingly dominant immediately, if not inevitably. They won titles in 2017 and 2018 and were only stopped in 2019 by season-ending injuries to both Durant and Klay Thompson. He and Curry formed one of the most dominant pairings in league history, and both were viable MVP candidates leading the most dominant postseason team since Michael Jordan's Bulls.
Durant then hit free agency in the summer of 2019 and could have re-upped to form potentially the greatest dynasty in NBA history. Instead, he took meetings in free agency and strongly entertained leaving.
Stephen Curry was on a plane heading to meet Durant for an in-person meeting to try and convince him to stay. Rather than give Curry the respect of a final conversation, Durant's team announced he was leaving for the Brooklyn Nets while Curry was on the plane. It was an unnecessarily nasty way to end his time with a team that brought him the only two titles he has ever won.