What was the most significant moment in the history of Barney and James' relationship on How I Met Your Mother?

Barney and James' relationship on How I Met Your Mother was a unique and special one. They were stepbrothers, but they had a bond that went beyond that. They were both loyal to each other, and they always had each other's back no matter what.

However, the most significant moment in their relationship came in the Season 9 episode titled 'The Rehearsal Dinner'. In the episode, James reveals to Barney that he is getting a divorce from his husband, Tom, and he is going to bring his new boyfriend to the wedding.

Barney is initially taken aback by the news, but he quickly comes around and supports James' decision. In a heartwarming scene, Barney tells James that he loves him, and that he will always be there for him no matter what. The moment is significant because it shows just how much Barney and James' relationship has grown over the years, and how much they mean to each other.