No matter what context or capacity it was in, the relationship between Bucky Barnes and Steve Rogers was too important to ever let go. They couldn't lose each other, and because of that they'd both been doing what they had to in order to get to a place mentally and emotionally where they could be friends again, and brothers. Were they not both as committed to each other as they had been and always would be, it never would've worked.
Just as it would be harder for Steve to hear about Bucky's relationships, it was hard for Bucky to hear about his. But he was in a position now where he felt it was going to be necessary. If they were going to be the best of friends and brothers, then they needed to be able to share everything with each other again. He didn't want to just be Steve's friend on the condition that they leave out their romantic partners. That wasn't real and it would be denying themselves and each other of a genuine connection. Hard as it might be, they needed to cross that bridge together.
"We'll see who drinks who under the table. Think we both know you're the light weight," he teased.